For anybody who is interested the memory region for the Museum catalog is located at:
[heap+AB211184] (ver 1.1.2a)
or
[Museum Catalog Starts Here]
04100000 AB211184 0000xxxx
Im not entirely sure how the game timestamps your donations. The 2 byte values are mixed in there with the list of fossils/fish/bugs (which are listed in chronological order from the time you donated them). I couldn't successfully add a fish/bug without already having a present datestamp, and I couldn't successfully alter the timestamps, but as long as you have a current timestamp (just donate 1 thing on any given day) anything you add after that should show with the same timestamp/donor.
You could in theory make a loop cheat that's a cleaner cheat than using a convoluted inventory cheat and having to manually turn everything in, but since all the values for items in this game are all over the place, it would be an equally convoluted cheat, just minus all that handiwork involved with the old museum cheats.