Sorry, there is no way to unmap all FX Chain parameters with a single command. I’ve made a ticket to look into adding this feature, but I cannot say when or if it may be added.
One solution or workflow that may work for you is using Functions. This way, you can always use the same MIDI CCs to control Functions 1-8, but in each project Functions 1-8 would control different parameters.
If you have a front panel unit, you can press the Parameters button, and then go to Functions > Map and this will show you a list of all the mappable parameters in the currently selected FX Chain and which Function they are mapped to. This would make it easier to see which parameters are mapped, but this view is not available in Emote, you can only see this on the front panel.
Let me know if you have any questions.