When it comes to finding synonyms for "pre-fixed," there are quite a few options. You might try "prefixed," which means essentially the same thing. "Attached" or "added" could also work in many contexts. "Combined" or "affixed" could be good choices if you want to convey the idea of two things being joined together. Finally, if you want to emphasize the idea of something being put at the beginning of something else, you might consider "initiated," "introduced," or "incorporated." All of these options could work well depending on the specific situation and the connotations you want to convey.