I just cut the bolts down if I need to...If you worry about getting them hot, the just use a hacksaw and dress them with a file. You have to get a bolt very hot before it will change it's strength characteristics..
I used a sanding disc on my angle grinder and had a spray bottle of water to quench every couple of passes. All 4 bolts are on and torqued down, blue locktite used. Glad I have that behind me, now I get to weld up the exhaust.