Mentioning it at the plate meeting does NOT constitute the first (and only) warning.

Cover it generically under "legally and properly equipped" and give a warning only if needed during the game.

Understood... However I also try to make my pre-game short and to the point and the jewlery seemed logical to delete because they didn't enforce it until after I warned a player in the first place... Just me. Also seems as if each association has their own POI and it doesn't seem to be very important here (this is my first year in this association so i am still learning the ropes here)

Not to mention that we have to. Here's my plate:

[Introductions and Line-ups]
"Are your players properly equipped, including no jewelry?" (wait for yes)
"Okay, [Home Coach], take us around the field." (wait for completion)
"I'd like to emphasize good sportsmanship at all times. Are there any questions?" (wait for q's or "nope")
"Great. Let's have a good game, coaches."

Has anyone ever answered "no" when you ask if everyone is legally equipped? Has anyone ever sneered, "So what?" when you gave the sportsmanship spiel? Both are a waste of time.

When the NFHS or my association is my employer, they can tell me what to include in my plate meetings.

Introductions, lineups and ground rules are all I ever cover at those meetings. Uniform, equipment and behavior violations are dealt with appropriately if they are observed.

As an IC, you agree to follow the rules and regulations set forth in the contract. I'm sure the contract includes following the rules of the league you're umpiring. NFHS is, somewhere in the chain, the rules of the league. Therefore, you are told, through NFHS rules, to include both in your plate meeting. Declining to do so is, in effect, a breach of your contract.