Yep the bolts are the hardest part if they snap off, don't waste your time trying to drill them out. Use a big C clamp a socket and some heat to press them right out.
Heat is the best for loosening the nuts. You have to get them cherry red and then they'll come right off. Use plenty of copper based anti seize on them when reassembling and you'll never have a problem again.
The best way to drop the muffler in the back is to just unbolt the the top mounts... Same with the center mount. Transfer everything to the new exhaust while it's off the car.
If I remember right you can do the trans mounts without touching the exhaust...
Dinan CAI &Throttle body, ESS Tuning TS2, Bimmerbrakes gen3 headers, UUC SSK & DSSR. Achilles oil pump, VAC oil pan baffle
M3 Motor mounts, UUC Trans mounts, Modified clutch style LSD 3.15, TMS front subframe reinforcement, Koni Yellow sports,
H&R sport springs, UUC sway bars, BMW Perf. Rotors, UUC SS brake lines, Hawk HPS pads, CSL replica wheels,
Rotora strut bar, FXR HID conversion, M3 Mirror conversion, BSW stage 1 speakers