I wire in the new/replacement ballasts in flourescent fixtures (4' and 8') at work all the time with the circuit running...the important thing when doing that is two-fold...
#1.) Make sure you disconnect the hot lead first and wirenut the end and tuck it OUT OF THE WAY of all the other wiring your futzing (sp?) with...
#2.) Then, I snip off and wire back up all the OTHER WIRES before going after the hot lead LAST.
The important thing in all of this is: IF YOU DON'T FEEL COMFORTABLE DOING THE JOB YOURSELF, GET AN EXPERT IN THERE...FAST! Make sure that whoever you have doing ANY work for you is licensed/bonded and insured.
Otherwise, your abode is theirs...or at least, the attorney they/their survivors' have hired. Even if your SOB BIL/SIL's bro. is on the job. And for Dog's sake, if ANY alcohol has been near/consumed/thought of, DO NOT EVEN GO NEAR THE AC PANEL OR SOCKETS.
(I've already discussed the repercussions on that circumstance...) 
