Sometimes it's hard to find any love :blinking:
40% or less won't cause any harm to any of your stuff, and there's no issue with using the same regulator for nitrox up to 40% sometimes and plain old air at other times. The only possible concern might be with a tank, in case you get it filled at a shop that blends in pure oxygen to mix the nitrox, which is called partial pressure blending. If your shop does continuous blending though, or if they fill from a nitrox bank, then O2 cleaning the tank is not necessary, and you can use the same tank for nitrox as you do for standard air fills.
If you own a tank, and if there's a chance you'll get nitrox fills from a shop that does partial pressure blending, then your tank should be O2 cleaned and you have to be sure not to get fills from any source that's not ultra clean, or else it compromises the cleaning. I don't think that many places do partial pressure blending for nitrox any more though, so you're probably good.