Ward Spoilers - Tumblr Posts
Oooh I like these, so I'll chime in, but the short version is: No.
But the long version is: No, because.
1) In the case of second trigger causing a cluster, we need to understand how clusters are forming in the first place, how second triggers function, and then why for both of these things. Why is the shard clustering or going through a second trigger?
For the latter it's simple since we only have one example in canon, Brian, and in his case it was because his power wasn't solving his monkey's paw. This isn't the same thing as his power being useless or powerless in the situation, I'm sure plenty of brutes have been eaten by the Siberian and their power has been useless to save them. The crux actually is that he's being thrust into the same mindset as he was in his first trigger. Trump aspects are being added, because this time the threats are parahumans, and his little-sister stand in is about to have a fate worse than death inflicted onto her.
There's also a completely new paradigm to his trigger dilemma; he needs strength, any kind of strength, from any kind of source. His own isn't enough, it's never been enough. Nothing he has or has learnt can keep Taylor safe from all the shit she's been throwing herself into. Before it was fine if he had a way to hide Aisha from malicious intent, hide himself from violence, but now he needs something that can adapt to any kind of power that might harm himself or Aisha or Taylor or the other Undersiders. So if he can't rely on his own strength, he'll borrow others. Stranger/Trump shift, losing a bit of Shaker because its no longer a dangerous environment (just bad situations they keep falling into) but a dangerous group of parahumans he's defending himself from. His monkey paw has shifted and his trauma has taken on a new aspect. This is why he moves on from Taylor, who rejected his leadership and took it out from under him whilst he was suddenly granted power over other parahumans, and also moved on from her romantically, going for the anti-Taylor, a big breasted professional thief who prefers low stakes.
Now we've explained why and how second triggers form, lets look at Clusters.
Why do Clusters form? It's not because the Shards are all triggering at the exact same time and getting 'tangled' in each-other. It's because they're actively choosing to collaborate with each-other. It's not a simple thing to orchestrate and it involves an intense amount of cooperation, something some shards don't quite like at all (see Grasping Self in Ward). It's not an automatic thing either, I bet plenty of people were triggering in Japan when Kyushu sank, but Lung didn't cluster with any of them. Shards can trigger without clustering.
It also doesn't take too much of a leap to suggest that adding new shards to the cluster, which is usually already 3-4 members, wouldn't be something the other shards would accept. Firstly, all 3-4 original members would have their powers readjusted or weakened once again to spread to the new member, and the new member's shard would also have to weaken it's host and grant powers to the cluster. For a shard that has already invested a lot into it's host, enough to second-trigger in the first place, rather than just let the host die and move on to a new one, this is a pretty tall order.
However, a newly formed cluster trying to involve an already established shard/host might be possible. There's nothing in the canon to suggest it's possible though. Nothing to suggest it's impossible either.
2) We have no evidence of clusters ever having second triggers, and there's not a lot of sense that they would. In the first place, cluster triggers are already a heavily involved process, reproducing a clustermate's trauma to a sufficient level to cause a second trigger is a tall order. Consider also that they're not like our second trigger example, that they have a single power that needs tweaking to suit new circumstances, they instead have multiple minor powers that would all have to fail in order to call for tweaking.
But then that runs into the main conceit for some clusters; sometimes clustermates must die for interesting data to be gathered. Sometimes, it's a highlander style fight to the finish, sometimes it's trading tokens for power boosts, which practically suit your question. I'm sure plenty of writers have introduced concepts like clustermates eating each-other to imbibe their DNA and therefore their powers, strengthening their own, until there is only one survivor with 4-5 major versions of their powers.
It's therefore a little counter intuitive to change the powers of a clustermate when they've reached a fail state in the experiment and will probably die soon anyways. To answer your question, if their powers were to change, I think it'd be their main power only, if their shard even bothered to do something about it.
3) Okie, so clones and twins. We've seen that clones' powers can be identical and can also be tweaked to cause different effects. See S9k and Echidna clones respectively. We've seen that twins can have either extremely similar powers or radically different powers. Fenja and Menja in the former, Tristan and Byron in the latter. Why did Capricorn go case 70 where Fenja and Menja didn't? I suspect it has something to do with their triggers.
I think Fenja and Menja had the same trigger trauma, but that meant that the shard could distinguish between them, because they were both generating data. I haven't read a lot of Ward, but I think because Tristan and Byron's trigger trauma was different, the shard was getting fed conflicting data from the same genetic match and had to choose between keeping them separate but with the same power or merging them and getting two powers.
I think any kind of clone parahuman is unable to have a second trigger for the same reason Taylor couldn't have a second trigger. The power is already experimenting with some new power bandwidth, and Echidna's broken shard was helping somewhat with generating new criteria to create things like Chitter and Scurry, but it doesn't get to then receive the new versions and tweak them for later. They're disposable compared to the original host. A 'what if' to keep the original on their toes. All of the Echidna clones get killed in the end anyway. S9k clones were designed by bonesaw, so I can't really say that they're running off the same rules as their original parahumans.
To answer your question, the canon example of twins who had powers but weren't case 70s would be Fenja and Menja, and I don't think twins can second trigger while they're still alive. Again, the monkey's paw has to come into effect. I could see a case where the surviving sister second triggers without her sister, and it draws her dead sister into herself and you get altered powers and a case 70 situation. For Fenja and Menja, they could become Hel and get moon/sun, night/day alterations on their powers, but their powers are getting big and durable so I don't really know how you can riff off that. There really isn't very many problems they can't solve by getting bigger and more durable, not without that problem completely overpowering them before they can second trigger and killing them.
My headcanon here is; if there's only one twin surviving, they can second trigger and maybe end up with a case 70 situation where the dead twin comes back.
So what's the very long version? Yes, you just have to know what you're writing as an exception. I think all three of those should be allowed and would be very interesting.
Second trigger Questions
I've read both Worm and Ward twice now and I loved both. I just have a couple of questions about second triggers.
If someone where to have a second trigger right as some one else was triggering could they become a part of a cluster?
If some one is in a cluster and they second trigger does that effect their cluster mates and is it only their main power that is changed or all of them.
If twins who were not case 70 capes second trigger next to each other could they become case 70s?

I can see Amy hating herself enough to have an amnesia inducing meltdown. Calling Victoria through muscle memory and being too shocked and grief-stricken to talk when she answers. Mourning the living. Deifying her love and putting an ideal version of her on a pedestal. Awful yet sincere karaoke. A binoclard torque-dork with plenty of empathy would fix her I agree. Would she be a Sorry Cop?
People say that Amy Dallon is the Shinji of Parahumans, but I declare that she's actually Harry Dubois. I will put this theory in practice the moment I figure out how to write a quest fanfic.
hey what the fuck is up with Ward?
If Nursery wasn’t such a fucking creep, I’d feel bad for her literally having the definition of “my power is to sexually assault you”. On a decent person, that is literally the ultimate cursed power to bear and like… never ever fucking use.
Like, there’s no way to go hero with that power in the first place, but goddamn if Nursery isn’t like, “Welp… time to forcefully impregnate people”.