That document only deals with headgear though. It doesn't cover the scenario of someone wanting to tape a religious necklace* to their chest.
The document on the link below (also from the Essex FA, interestingly enough) provides a much more comprehensive treatment of the issues surrounding religious jewellery and religion in the game in general.
Belief in the game
It also doesn't specifically cover the matter of taping a religious necklace.* However it does have the following advice.
*I have to say I'm not familiar with any religion that requires wearing a necklace. Bracelets (as mentioned above) yes, but necklaces? Difficult to say definitively that that's not a thing but I think that if as you say, your going to be encountering this player repeatedly, I'd be inclined to ask them (in a very polite and roundabout way, of course) which religion it is that requires this. I'd be interested in the answer.
But in the end, as the document linked to above says, it's still up to you as the referee to decide, based on safety considerations, whether you're going to allow it, even if you accept it as being a religious requirement.