The only solution to your problem is dodgy
not knowing the bike intimately or your choice of muffler i will assume that you can remove the factory unit without cutting and also fit the aftermarket one with clamps
1/ carefully tape around the area of the clamps to prevent tool marks and remove the original part
2/ fit the aftermarket muffler
3/ store the original in a place that it will not get damaged
4/ refit original part before going back for servicing/warranty work