I'm pretty sure that you can afterbang if you want. I know that I do, sometimes, just because its fun... and I only ever afterbang spread eagles and other sick-as-gnar tricks like that.
b4 bang has existed for a long, long time, in a less exagerated manner- it's been known as an ollie, guys.
And midbang would just look like a backscratcher, one of the tricks I like to afterbang.