the Q change would probably be way stronger than the E change to be honest. Missile speeds are one of the hidden strengths that abilities have that many players overlook.
As for the E, I don't think it would be too overpowered if you split the damage into components like you do with poppy's charge and vayne's condemn, and change the stun into a root, considering how this is an aoe non-ultimate ability.
My problem with the e change however, is that it doesn't seem to add any synergy with his kit. Galio is currently good at getting in with his q to slow the crowd into e to boost himself into the middle of the enemy team (when he doesn't have flash). if E now pushes enemies away his ability to get in becomes, surprisingly, a little bit more limited, because pushing the enemies away from you makes it more difficult for you to get in for an engage. Enemy caught out of position? you actually can't E and walk in like you used to be able to because you're giving the enemy free distance to run away.
Of course, this mechanic isn't a bad one, per se. Obviously there are the situations where you get pins, and when you use it to push chasing enemies away, but this introduces another problem; do i use this e to speed up my allies or push the enemy back a bit? There may be lots of use cases where the galio player is presented with two options that seem equally good, but not completely satisfying. Having versatility in a kit is fine, but personally i feel like a kit where you know exactly what the correct play is given a situation is much better, because you don't end up feeling like "oh, well i guess i should have done _____" if the play falls through.