That caution light is there for a reason. Operation off the ground with the prop in the ground range is unsafe, unwise, and not approved. In fact, only a handfull of installations in the world have ever been approved for any kind of reverse or ground operation in flight, and your aicraft isn't one of them.
Again, you feel that operation in ground idle, a fuel controller function that presents NO safety of flight concerns, could cause you big legal troubles because you *think* it's not an approved operating condition. It is an approved operating condition.
Conversely, you're willing to enter an unapproved engine operating condition, bringing the power lever over the gate into the ground range, and don't seem the least bit concerned about the safety or legal implications.
Write to the manufacturer and ask if they approve it. Let me know what your response is.
No "slanging" necessary.