One bitten, twice shy. Paranoia is just reality on a finer scale.
Unless you specifically turn off the feature, any admin that touches a GPO will replace the ADMs on sysvol if they have newer ones. If you modify an ADM it will have a newer date and it WILL replace every GPO you touch. I had a French admin screw up my GPOs because he modified his ADMs and his French ADMs overwrote mine.

When MS updates the ADMs through a newer OS or SP, they too will (may) automagically overwrite your custom ADMs. Laugh if you will at my paranoia but I might have the last laugh.
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Give a man a fish and he will be back for more. Slap him with a fish and he will go away forever.