Cam-
I replaced the fuel pump on the M25 in our C30 many years ago. I believe I simply shut the fuel supply off and crimped the fuel lines near the pump to minimize introducing air. I don't recall have to bleed the fuel system after the pump replacement. Perhaps I got lucky. 

My mistake- I thought you were looking for fuel pump info. I've not replaced an injector pump. The below link might be helpful for you:
https://forums.sailboatowners.com/threads/universal-m25-fuel-injector-re...