This is kind of an odd request, so if the premise is too odd or flimsy don't worry about answering! But I seem to remember at least some mention of Matoran occasionally changing their home Metru or Koro: for example, a Ga-Koran choosing to live in Le-Koro as a Le-Koran. Are there any Matoran words you might use to help describe this sort of change or transition?
Not odd at all! Believe it or not, this is something I've thought about for a bit, even though I don't think the concept is ever really addressed in-story. Here's my take:
I would classify the Matoric word for the kind of state-change anon describes as referring to the same function as "Naming Day" in Matoran society, where modifications to the "name-designations" of individual units within the MU system were officiated by Turaga. Tribal associations could be similarly updated.
There are two terms that would be relevant to the concept of one's designation within the MU (which I refer to as the Mata System).
The first is akharo "system-designation", referring to one's official "name" and possibly purpose/function in the Mata System. It is formed from the elements akh(o) "system, structure; law" and aro "designation, individuation". In a verbal use (akharo ya), this can mean "designate a name" or "designate a function", and since alignments like "being a part of the Le-Tribe" or "being a part of the Ga-Tribe" are associated in the Mata System with different functions and tasks, akharo can also describe the alignment of a Matoran with one of these groups. I haven't considered there to be any significant distinction between an "initial" assignment (say, at the creation of a Matoran) and a later assignment.
The second term is a bit more specialized and has some associated implications. The term is Arua or Arwa (also found as aru, airua, and herua, depending on the dialect) and it is an older term than akharo. It is also formed on the basis of aro "designation, individuation", but this time in combination with a very obscure marker ua "agent" which signifies a kind of agentivity that is normally restricted to the head of the Mata System: Mata Nui or sometimes the Great Beings.
In other words, arua/arwa can be translated as "designation by Mata Nui/GBs". The term has a bit more weight or importance in that sense, implying that the designation is not just officiated by a Turaga; it is deeper and more powerful within the Mata System, possibly implying something about the target's nature (i.e. "this individual is not just associated with X tribe right now, maybe subject to change at a later date--they are now an integral part of that tribe, by 'Mata's decree'").