You're wise to ask. Forever stems offers acrylic stems for Missouri Meerschaum pipes that fit well and can be shortened to length if desired (or that was so when I bought mine). These eliminate the filter on filter cobs. With most briar pipes, the fit is a little more specific. Some manufacturers offer replacement stems, but they will not always fit exactly. If you value a pipe, you can often get a good custom fit by a pipe repair pro, and for not a lot of money. You can go from Vulcanite to acrylic or the other way, or from P-lip to fishtail or the other way. I have heard of people picking out a usable replacement stem in the odd-lot drawer of a pipe shop, but I suspect these are make-do jobs and not necessarily a great fit. So yes, you can replace a stem, but you may have to work at it.