Updating isolated UV pieces without changing the whole UV map?

I am working on a set of windows of different sizes, but I am limited on time and doing optimization work to make it as fast as possible.
What I thought of doing is modelling the biggest piece, do the UV work there (I do it manually for ease of reading purposes since just UV wrapping without any additional work makes a big mess that I can’t read and work properly with), thinking that duplicating the model and then editing the model on specific parts would update the specific UV pieces without changing the whole thing, but turns out nothing changes on the UV side, as the individual pieces are horribly stretched texture-wise in the 3D view, even if I check “Live Unwrap”.

Is there a way I can accomplish this without having to do manual UV work for all the windows pieces?