I never tought toasting black pepper was worthile, seem it is to some extent (higher heat degrade piperine?), see here https://agris.fao.org/agris-search/search.do?recordID=US201600056763

It's probably better to toast when you need them but you could give it a try and see for yourself how it evolve over time. There is science but it's also a qualitative / sensorial. Maybe you will find that it's good a x days or weeks and that it will be good enough for you instead of prepping it everytime.

I would probably give a shot to sous-vide freezing also (what I did with fresh green peppercorn found at asian market for thaï recipe instread of using brined ones), you could use a manual grinder you keep low for that special pepper or use electric grinder or mortar.