LVL down?

it worked on 1.26 with cheat engine but that can get u banned for sure

You can delete your character and find a hack that Increases your level and money and unlocks what you want. Basicly the same as deleveling but with a bit more work.

You can delete your character and restart leveling up with cheats, it will be fast and easy.

You can't, afaik there's no situation in game where you actually lose RP.
To have such a function in hacks, it would have to be implemented serverside first, then find one/multiple function(s) to reduce RP, but it doesn't exist in game.
So, unless you know a situation ingame where you can reduce your RP, the only way is to delete your char indeed.