Its just a really bad idea. Period.
Its likely not ever going to be a supported workflow.
Is it faster? Yea. Im with you/them on that.
Maybe just change/make a bluetility script that duplicates and places level instances at the correct inverted X/Y/Z after giving them the correctly calculated inverted rotation.
A day’s work to make a tool your team can use still beats the extra work having to manually place all the mirrored stuff…
And it gives them the ability to fully change/customize and replace stuff as needed without having to go trhough hoops and normal changes etc.
And in case its not clear - yes, you can programmatically add rotated instances to foliage or HISMC or anything else - so long as you code up the system to do so when you click a button.