Never got any crash while changing my TPC picture, so yeah that's weird !
I don't know if Romfs builder encrypt it back, I don't think so... it's just meant to repack the romfs file.
ACNL have updates or it's still the 1.0 version ? Because HANS doesn't read update, and I heard that our EU/US games aren't the same as JP games (our games are "patched", because there was a duplication glitch on jp games). That could be the reason why it freezes
I think is a problem with Hans.
I've done modifications to my Pokémon X but I can't do the same with Animal Crossing, is always freezing in the title screen.