Yes, you can change just one sound in a layered worship patch in Sunday Keys.
The simplest way to do this is to pull up the layered worship patch you'd like to change, and then take a screenshot of it so you can replicate the sounds and their modifiers' positions by creating a new Patch in the Patch List with the sounds you do want:
- Take a screenshot of the patch you'd like to adjust.
- For example, I might like to change the pad to Gentle Pad instead. So now, add the patches you need from Patch Builder to do that and the combine them - Section 1: SK Grand | Hall, Section 2: Gentle Pad, Section 3: Regal String Pad, Section 4: Trance Lead, Section 5: Synth Bass. You can search through the Section Folders > View All to find them, or you can choose ⌘F to search. Do not change modifiers as you go, do that after combining them together into a patch.
The video below will help you work through how to combine sounds to make a patch if you need further help: - Now that you have your new patch, adjust modifiers from there so they match your screenshot, and make any further adjustments by ear so you're happy with your new patch, and you're all set!
If you'd like to learn more about using Sunday Keys for MainStage, be sure to check out the videos on the Sunday Keys Resource Page.