I have created a custom interface that has symmetry options on the shelf. I can load that interface at any time, but it won’t load the editing functions unless you’re in Edit Mode at the time that you load the interface.
The reason for this is that when features don’t apply to your current choices (like being in Edit mode, or having a polymesh selected) then those interface items do not exist at all. As a result, ZBrush can’t load them into the interface when you load the interface itself.
Here’s my recommendation: Create your interface and save the configuration to ZStartup\UserInterfaceLayouts. Then when you launch ZBrush, work like normal. When you start to do something that needs the layout you created, click the Load Layout buttons found in the title bar (their to the immediate left of the Lock icon). That will bring up the interface you created, and because you’re already in edit mode it will contain everything you wanted it to have.