1/2" acrylic doesn't come in roll stock. (think of how big the spool would have to be)
I've cleaned thousands of pieces of acrylic with iso alcohol and have never seen it affect the acrylic. I've also applied lots of graphics with rapid tac (on acrylic) and have never seen it crack. Flamed edges, shape cut, holes cut, straight flat cut etc.
What brand of acrylic are you using? Worst case scenario you can prep with just water/drop of soap but I like to soak the whole face down with alcohol so you get that good "bite".
Another thought/possible workaround - why aren't you mounting with a laminator? If you have a half decent laminator it will mount to 1/2" acrylic no problem. Depending on the panel size and if it's extruded, I have seen larger/thicker panels that obviously weren't 100% true in thickness, where the vinyl wasn't pressed all the way down across the panel - but it's only happened a couple of times. I'd say it's worth a shot rather than ruining more acrylic. If you're using something like 3651 clear it will lift up without leaving adhesive as long as you strip within a couple of hours.
Hope that helps - any questions let me know.