Speaker repair...is it easy?

It is not that difficult but you will need a good surround adhesive and some patience and some knowledge and experience otherwise you could make a mess of the surround and the cone.

+1 millercarbon. It’s not that tough. Keep it centered as best you can and you’ll be fine. I did this to my old jbl l300 and they’re still golden after 10 yrs.. Watch a YouTube vid on it. 

I'm not sure it's something that should be attempted. Even the slightest deviation off axis or a minute uneven tension could be enough to compromise the sound.

Just being cautious.