How hard is it???

It doesn't appear to be too difficult for a Mustang. There really isn't a whole lot holding those bumpers on to the car...those two plastic collared screws under the hood (at the grille area) and the grille itself, if you have one. Then maybe a few bolts underneath and a couple screws in the wheel well.

I helped a friend do some headlight work on his Mazda 6 a while back, and to get the headlights out, the front bumper had to come off. We did this work a couple times since he kept finding different tweaks for it, so I managed to get the process of taking that bumper off down to about 5 minutes. It was all of 8 bolts and screws total. And the first time I did it, I just went around looking at various attachment points...didn't have any instructions to go off of. Tool wise, I just needed a Philips head screwdriver, 2 different sized sockets, and that was it. If you have someone to help you, that would be a big plus...they could hold it in place while you get the bolts going once you're ready to remount the bumper. You may also want to take the bulbs out of the foglights beforehand, if applicable.

Based on that, and from me seeing the inside of my Mustang's bumper a couple times (don't ask...LOL), I would say it's not hard to get the front bumper off.