Are you sure about them being Brown? Last I checked, the Steelseries used Black switches. Black = high force and linear. Brown = low force and tactile.
Either way, it is possible to swap switches by de-soldering the old ones from the board and soldering in new ones. The different switches are electrically compatible so there's no more effort required there.
Swapping switches from other vendors is for all intents and purposes impossible, as the circuitry has to be adjusted to deal with the specific type of switch. The exception to this may be some Cherry-like switches like the white SMKs.