As a rule of thumb when you are doing development adjustements you should change the EI if you have done the necesary testing. In my experience I have seen the EI changes with the zone system to be lower than when you do the BTZS.
EI changes are also different for Tmx films than for regular films. Seems the Tmx films require smaller changes than a "regular" film.
In any case I do change EI depending on the SBR.