While Minecraft is launched, resource packs can not be configured. This makes the "reload textures" F3+T not helpful, and the game must be closed before even being able to configure the pack.
Linked issues
duplicates 1
Comments 4
I believe that this restriction only occurs with zip folders for resource packs; resource packs that are just regular folders and aren't zips are still editable.
Urilsalis: Even if I unload the resource pack, if it was previously loaded, it's still locked
Pokechu22: Aren't resource packs only recognised as .zips? If it's a normal folder will the game still recognise it?
Does it work if you select another resource pack and then load the resource pack again? It might be intended as the textures are loaded