Do all SB scenarios begin with fixed setup?

[rahamy]

All the scenarios start that way, so players can just dive in and start playing.

With that said though, all the games come with a scenario editor so you can open any scenario with it (or create a new one from scratch) and rearrangement the placements as you see fit. Make sure and save the file with a new name though so you don't loose the original stuff - or have your work over-written when a patch is applied.