For this particular pack I have personally downsized some of the larger environmental texture folders by 33% and left other elements such as the UI, characters, effects, and other smaller folders untouched. As such they seem to freeze (for me, at least).
OBSOLETE INFORMATION (12/5/19)- Mupen64Plus NO LONGER HAS THIS LIMITATION Some texture packs larger than 1 gigabyte, such as the Majora's Mask N64HD Project, seem to approach the 1.5 gigabyte texture cache memory limit for Mupen64Plus.Quit Retroarch and restart the program and rom.Enable Use High-Res textures and Use High-Res Full Alpha Channel - note that I personally had to toggle these a few times after quitting Retroarch but they eventually worked.While the ROM is loaded, select the Quick Menu and go the Options tab for the core.
Enabling the Hi-Res Textures in Mupen64Plus:
