It all depends on the round. It will take some 'trial and error' on your part but it will change the ballistics of the bullet path because..
The muffler directs the gasses escaping from the muzzle as the bullet passes through the muffler in a different direction (usually outward into the packing) so flight characteristics of the projectile are altered. Instead of the gasses following the bullet path, they are mostly removed/redirected. Just like a muzzle brake. If you shoot without a brake and install a brake, the ballistics change. This will really come into play with long range shots.
I would imagine some issue in changing from a brake to a muffler for different situations. Will probably take different loads for each scenario, brake, muffler and nothing, not that I'd be keen on lighting off a .338 with a bare barrell. The recoil would be punishing......
Not to mention the adverse effect on optics.
It's very possible to actually build a 'homemade' muffler from PVC tubing, disc packing and some ingenuity to give you an idea of just how much of a change there will be before shelling out the bucks for a factory muffler.... Just be discreet and don't show anyone.
There are also other inexpensive options out there, however, the letter of the law is very explicit. Better to not circumvent the law.
I know nothing.........