Yes you can over fill. The result will be dragging brakes of to the point of locking the wheel. It is somewhat common to have the rear lock up after brake work when it is over filled.
What happens is the brakes drag slightly, maybe not even noticeable, but that creates heat. As the fluid gets hotter it expands, the only place to go is to push the pistons out of the caliper, this makes not heat more expansion......... You will first notice what seems like a loss of power untill the brakes finally lock the wheel. If you have a bleeder wrench with you, you can simply crack the bleeder to relieve the pressure and be back on your way.
Or just bleed a bit of fluid out until you are at the correct level and not worry about it until you get the screws fixed. But DO keep a wrench to fit the bleeder screws stored on the bike just in case.