The phrase "set in stone" often refers to something that is unchangeable or predetermined. However, there are several synonyms that can be used to convey a similar meaning. For instance, "fixed," "unchanging," "immovable," or "rigid" all suggest a lack of flexibility or the notion that something cannot be altered. Additionally, "etched in stone," "written in stone," or "carved in stone" all incorporate the idea of permanence or finality. Using any of these alternatives can provide a fresh perspective or alternative phrasing to convey the same idea as "set in stone".