That would make it too easy //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
Best case - your amp has decent protection, and only blew a fuse if it's really protected...or only a Zener diode, which is a relatively straightfoward task to desolder and replace.
Worst case - your amp didn't have any sort of protection, and the reverse polarity killed some FETs and damaged PCB traces...
That's why you never, never, never, never work on a live circuit //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Disconnecting the negative lead would have prevented this from happening...