I have replaced the levelers on my games with nylon pads to protect my tile and wood floors, but they are hard to find. I recently took a game to a friends house and set it up for them. I could just imagine the worn metal levelers leaving rust stains on their white carpet. After a bit of a search I found the ideal caster for protecting your floor with out changing the levelers. They are hard plastic and not too grippy.
https://www.amazon.com/Furniture-Durable-Surfaces-Protect-Protectors/dp/B004670YB8/ref=pd_nav_hcs_rp_1/136-4381762-9509915