Given the popularity of Mina the Hollower recently, I've been surprised at how few mods and tools were created for, especially a quite usual one for this type of game: a sprite editor.
I have just recently completed a tool that allows injecting a sprite sheet into the game, with a template sprite sheet available in the download, which can be found on GameBanana here:
A Mina the Hollower (MTH) Modding Tool in the Other/Misc category, submitted by EpicGamer10075
There are some current limitations to it, such as a limited palette, only working with Mina's sprites, and not being able to change sprite size or animation data, but for a simple sprite swap job, this tool should do the job!

















