Minecraft textures from Modpack?

I wanted to ask if it is somehow possible to pack textures from a modpack into a normal texturepack.

You go in the mod folder, look for the textures for example earth block and replace it in your texture pack with the earth block

Unfortunately, that doesn't mean exactly what I forgot to write in, I would like to have certain swords, but these are connected with JSON files or something and I have no plan how to do it.