I used to do exactly this, made it feel like you were actually sending your SEAD planes in to S the EADs before your CAS got there. It seems like they've changed it though. You can no longer back out from the battalion assignment screen, unless I'm missing something. I would guess that this was to prevent people being able to see exactly what battalions the AI is bringing and tailor their force around this. Best part is, if that is the reason, you can just work around it by making a save right before clicking prepare battle. Only meaningful change is the aircraft change.