Honestly, with something as specific and unexplored as this idea, I think you can do whatever you want. As for plausibility, it sounds just fine to me. The only thing is, if you want those three nodes to form a converging beam like they would if combined with the other five, you’re going to need a cone-shaped forcefield in the middle. If not, it should function more or less like a powerful individual laser.
Now, if this is related to your other ask where you talked about getting a hypermatter reactor, I think it’s reasonable that it would barely be able to fire the beams and might have to recharge for a while. The reactor installed on the Death Star is an advanced version of the ones that other ships often have, so I doubt it would be able to produce as much power as the lasers and shields combined would like to take up.
It sounds like you have a very interesting story here. Good luck!
~ Jacen