Instead of having your pack as a .zip folder, have it as a regular folder. Just have the /assets/ folder right in a named folder instead of a .zip file, but keep everything else the same. Then, after saving a file into it, press F3+t to make the textures reload. The game will freeze for a second, and then re-render everything with the changes to the pack.
I hope that helps you.
Great tip, I knew about the folder instead of .zip but didn't know of F3+t