You can swap cages (both the fixed front side and bolt on rear side) which is what I think you’re getting at.
The cage should be held on by a 5 or 6mm hex key bolt and there is the sting behind it which is a bit fiddly but it can be done
Mentioned to him about the listing as it’s important info when he sent me pics earlier, it’s probably repairable but to have cracked in 2 places he must have USE’d a certain seatpost :)