Editing an External Mod's Assets

Hey, I'm wondering if there's any way to change a different mod's assets from within MCreator. To put it into layman's terms, I'm making a structure mod for Pixelmon Reforged that involves boss trainers with custom textures. The only way to get these custom textures working is by making a folder path that goes like this:

assets/pixelmon/textures/steve/texture.png

So, how would I go about doing that in MCreator? All I can really seem to access are the internals of my own mod and not anything else.