Unless he is certified to do warranty work on behalf of Omega, he would be voiding the warranty by working on it.
Are 321b's esoteric? No - I service them all the time. The narrative that Omega spins on these is to create a halo kind of product. The nonsense about the scanning of an original watch being needed, the fact that each watch is assembled by one watchmaker, that repairs can only be done in Bienne - these are just marketing ploys that people eat up like candy.
Watchmakers all over the world disassemble and reassemble 321's every day without issue. It's a bog standard chronograph - nothing elaborate or special in any way from a watchmaking standpoint. Assembling one of these using new parts would be a dream job compared to trying to get worn out beat up old 321's running satisfactorily...