Well, I did some more Google Fu and did rustle up an article MD wrote back in 2017 called Rifle Powder Temperature Sensitivity
In the article MD logged data for RL-22, which IIRC is equivalent to Norma's MRP, and joy of joys he also logged data for Norma 204. At least I think it's 204. It's referenced as N-204 anyways.
In any case, if I can read the data correctly, the N-204 didn't have a POI change due to a extreme temperature change.
So, the result of all this is I'm gonna swap the old feller's (who's headed for a retirement community) Norma powders for some backstrap and stew meat.