Hi @Matth, welcome to the forum 
There’s some relevant discussion of applicable failsafes in this thread.
Note that failsafes that cause the autopilot to disarm will affect outputs designated as motors, but that may be counter to your desire to control outputs individually.
That is new in the latest version, and was ported over automatically from other firmwares, so not something we’ve meaningfully tested with. I looked briefly at the code and ArduSub does at least use the library which defines the parameter, but I’m unclear on whether it actually makes use of it, and don’t currently have the time to test.
It’s also possible that failsafe only applies for real RC inputs, not RC overrides. If you describe what values you’ve been using for the related parameters and what control inputs you’ve been sending we can try to point out issues with your approach, or try to replicate it and more clearly determine how specific functionalities work.