It’s not difficult to replace at all. Remove the BAS & bolt handle, the firing assembly guts. Push out the bolt head retaining pin. Swap out the Ejector/Extractor, and everything back. May not have very good lug contact, but it should work. Sometimes, machining is necessary. However, this is not often from my experience.

However, fitting the bolt head is least of your concerned when you are inquiring about going from 223 to a WSM/SAUM cartridge.