Hi Alexander,
Yes, we routinely move to main theorems from other people's mathbox when we need them in ours. From my point of view, you can do it together with the addition of the new theorems in your mathbox, or, if it is a lot like possibly in this case, in a preceding PR. Feel free to do it yourself.
It seems unlikely that Jeff (of Frédéric) would like to resume working on those theorems, and I think we would strongly advise to use the new structures if they wish to, so I think it's safe to first mark them as deprecated.
From the chapter list, it looks like prime rings would be the last definition not yet converted to structures: I think we already cover all the rest (and Miss youch more, of course).
BR,
_
Thierry