I’ve heard that some people will do a rinse (filling the tank once with distilled water) of their film in between the developer and blix. Does anyone else do this? Does it help extend the life of the chemicals?
I don't know if a rinse between developer and blix can extend blix's life, but it can cause uneven development. An acetic acid stop bath can be used instead, which takes care of this.
I wouldn't recommend a wash between dev and bleach as it could cause uneven developing. Remember dev time in C41 is just 3min 15 sec, so it should go straight to bleach to stop further development.
Rom Mowbray (PE) recommended a stop bath in between the developer and blix. He also said to make sure it is a one shot solution to avoid contamination.