You can use bolts if you want, won't hurt anything.
I offer three points in favor of studs:
The studs should have a short threaded end and a long threaded end with an unthreaded spot between. The short threaded end goes in the manifold and either bottoms out in the blind hole or goes into the thru hole until the unthreaded part stops it. This locks the studs in place with maximum thread engagement in the manifold. Still a good idea to use some anti-sieze in case you do want to remove them in the future.
Use double nuts on the studs, again with anti-seize. I've found double nuts jammed together to be the most robust way to connect exhaust components while still being removable.
Bolts will have less thread engagement in the manifold and can't use double nuts.
Use studs intended for exhaust manifolds from the auto parts store. Should be better material and have the unthreaded portion described above. Hardware store all-thread is typically poor material. Sometimes the studs come with long brass nuts. These seem to work OK but I prefer the double nut method.
