Modular building with Identity block

I though I might be able to use the Identity block to copy-paste sections of spacecraft. This didn't work though, it would always replace my entire construction even if I left a gap so the identity block wasn't contiguous with the rest of the ship. I expect that's the intended behaviour but It'd be great to have some way to copy and paste modules.

By the way, thanks for adding middle mouse click to choose a block, that is extremely helpful.

Thanks to Cherbert for the suggestion on middle mouse to pick a block ! You can do CTRL-Middle Mouse to pick a color only by the way.
On the copy past yes this was the next command I wanted to implement. I will create a specific item where you select blocks around, then do copy : it will create a subset of all the block you selected to be build at once.