Switching Between Multiple Custom Backgrounds
Keep Separate Copies of the Pack
If you like changing your background often, editing the same zip each time gets tedious. Instead, make a separate copy of the Custom Background HD zip for each image you want to use, and give each copy a clear name so you can tell them apart. Replace the panorama_overlay.png inside each copy with a different picture, following the same path: assets / minecraft / textures / gui / title / background. Now you have a small library of ready-made background packs.
Swapping Them In-Game
To change backgrounds, open Options, then Resource Packs. Enable the pack copy that matches the image you want and disable the others, since only one should control the menu background at a time. If two are active, the one higher in the selected list wins, which can cause confusion. After switching, leave and re-enter the main menu or restart so the new texture loads. This approach also lets you keep a favorite default background pack untouched while experimenting with others. Store all the copies together so you can find them quickly whenever you want a fresh look.