If you ARE asking about recoil REDUCERS (not buffers), like spring powered inertial reducers or mercury reducers, then in general, yes, most long guns will accept a reducer, if you know how to install it (easy in wood, sometimes complicated in synthetics). Not all, not even many, firearms have them. Yes, they could be upgraded if it already has one, but I don't know why you would be motivated to do so.

If you are talking about AR-15 Recoil Buffers, then yes, all AR's have them, yes, they can be replaced, no, it's rarely necessary or beneficial. No, these cannot be installed in ANY gun; only in firearms designed for one.