Can I use a layered worship patch from Sunday Keys and change just one sound without rebuilding the patch?

Yes, you can change just one sound in a layered worship patch in Sunday Keys.

To do this:

1. Go to the channel strip for the sound you don't want and hit delete. MainStage will give you a popup message that says "Channel [name of sound] has #X parameter mappings. Are you sure you want to delete it?"  You'll click Yes. The sound you deleted will still be in the workspace, but greyed out.
2. Add the new patch in your patch list for the sound you want in it's place. So, for example if you deleted a Section 1 sound, you'll need to add the Section 1 sound you want instead to your patch list below the original layered patch.
3. Combine the layered patch and the new patch by clicking on the first one, and then command click on the second and select "New Patch from Selected Patches". You should see the new sound in that section now and be able to use your new layered worship patch. 
4. Export and save for later use!

If you'd like to learn more about Patch Builder, be sure to check out the videos on the Sunday Keys Resource Page.