It's not really possible in the Windows Store version of the game because the files are locked, but the Steam version can be modded:
SLX Studio supports the 4.0X version SLPs that AoE1 DE uses. With there being x1, x2, and x4 graphic sizes, 32 directions for units, and frame counts per SLP often being over a thousand each, it's not really easy to mod for the game. Mods would also probably need to have an installer that keeps backups of the files it replaces.[This message has been edited by Tevious (edited 01-09-2020 @ 06:50 AM).]