I haven't changed a front input shaft seal, because I've never had one leak enough to worry about.
For preventative maintenance on the M5OD while I've had it out for a clutch, I have removed the front plate to check the oil slinger, and pulled the top cover to inspect the internal parts, and to clean any trash from the oil trough (a plastic oil guide). In both cases, these items needed resealing anyway to fix small fluid leaks (I used RTV silicone gasket maker to reinstall both, although there is a o-ring type gasket for the top cover, I think).
I believe that you already have, and planned on, replacing the rubber shift rail plugs with freeze plugs. Highly recommended.
Hopefully others with more experience inside these missions will weigh in on your replacing the input shaft seal.
You're getting there.