ResourceStages
An addon for GameStages that dynamically loads resourcepacks based on your progression through different levels.
How It Works
Create or locate the resource_stages folder in your Minecraft root directory. Inside it, place subfolders named after your game stages where you should put the corresponding resources.

Demonstration
Operating Characteristics
Some resources and textures may not update instantly when changing stages. This occurs because many mods and the game itself cache textures during resource reloading. ResourceStages partially addresses this issue, but for complete refresh, press F3 + T.