Spring RTS Engine

I hold shift to drag a line of solars
I hold shift and alt to drag a square of solar

However I want to hold shift and space instead of alt to drag a square of solars,

How can I bind my spacebar to alt? Or is there a way to just change that particular square building widget - if so what is it called?

I put "bind space Alt", in a widget but it didn't do anything. Ty

Space is generally the spring "meta" key. I'm not sure if that might cause interference with rebinding it.