At my company, the official policy if you ask for a demotion is that your pay stays the same or is capped at the highest amount of the lower level.
I recently returned to work after a medical LOA and my performance was suffering, and my managers threatened to demote me 2 levels (as punishment) until I went to HR to complain. HR soothed the tensions and said I could ask for a one level demotion and get paid the same, and they'd HAVE to take stuff of my plate to justify the demotion.
It seems too good to pass up. Less work and same pay, although I'd be at the high range of the lower level so probably no raises. But I am going to FIRE soon so who cares.
The funny thing is that my managers, I think, wanted to demote me because I was already at the high range of pay for my current level. I guess they don't know our company's policies well. Ha ha!