Is keeping a red allergy morphine tag in my combat boot authorized?

40-66 be dammed if there is anything that shows and proves these Reg's are outdated is that field condition's override a Reg' that was made for a 'Perfect' Army. Post 9-11, all the way thru Afghanistan, Army Reg's have been found to be woefully outdated, and in need of serious revision. Many, getting Movement Order's, wasted no time in going off-post and getting these types of 'Red Tag's' made, and then adding them to their chain's, but also added to or stashed into, their uniforms and gear. Bear in mind that the purpose of these Red Tag's is to speak for you, in such an emergency, TO PREVENT ANY ACCIDENTAL DRUG'S OR PROCEDURE'S FROM BEING DONE TO YOU THAT COULD HURT OR KILL YOU. 40-66, in these case's, is a prime example of why these Reg's need to be up-dated, and for now seen reasons why, so that a Soldier doesn't get caught 'short' due to an outdated Reg' being used, when it should have been revised, or just scrapped out of commonsense altogether.

CPL Mike Kiernan .... Huh?

A red medical warning tag is worn around your neck. You also have the option of wearing a red medical alert bracelet.

So what exactly is your problem with what the regulation says? Of course regulations need to evolve and change, but I'm missing what your diatribe is against this specific one.
Your core issue seems to be that you might have an issue about where the placement of the tag is.

Not sure why there would be 'many' Soldiers going off-post and getting medical warning tags made on their own dime. They didn't have the ones they were issued with? This is nothing different that a Soldier needing dog tags. If a Soldier wants to get a dozen, more power to him. There is nothing wrong with someone having a dozen of these tags made and to put in it their pocket, socks, under their headgear, in their rucks and so on.

Regarding field conditions overriding non-field conditions. Absolutely agree. That's why, for the most part, regulations are guidelines for the commander. A commander is always within their rights to modify those guidelines for the safety of the troops, accomplishment of the mission or in some situation that they deem it is necessary (of course, if the higher-ups don't agree that they showed good judgement, they will be held accountable).

If the commander on the ground deems it necessary that wearing tags on the boots is necessary, he can absolutely change the on-ground policy. However, that is the COMMANDER'S call. Not every Soldier that thinks it's a good idea.

Col, the Reg's are written AS-U-MEEing that everything is going to go according to Reg'. Not gonna happen and we all know it, most specifically in these case's by the Platoon Medic's and the BN PA's at the Aid Station's. ANY TYPE OF RED TAG FOR MEDICAL PURPOSE'S is an increase in the information these folk's need to treat any casualty. And please don't tell anyone it doesn't happen since it does, at every Post. Off-Post in the 'ville's' there are any number of place's that make tag's, for various purpose's like this, many now for this express purpose. The std. Red Tag has been shown to be almost a joke for info', which is why the current ID Card was introduced w/ the RFID Chip, to aid in medical needs. But in the field a RFID chip is almost useless, which brings in the added Red Tag's to help. The Red Tag' regardless of how it's used according to DA Reg's, speaks for the Servicemember IN THE EVENT THEY CANNOT SPEAK FOR THEMSELVES. Such is why, and the MP's most of all know this better then anyone, these Red Tag's are the 1st thing looked for in the event a Soldier is unconscious at any scene and can't talk. These Red Tag's, regardless, speak for the Servicemember when they can't, something that far too many Commander's have a problem with when the Tag's are found, and Someone has an 'issue' with Reg's not being followed. Even the IG, doing their either Annual, a Spot, or a Pre-deployment, inspection is well aware of this and realize that this is an added 'insurance policy' for the Soldier and the Medic's to have in the event a soldier can't speak, when the Medic's need all the info' they can get to keep the Soldier alive.

CPL Mike Kiernan I still don't understand your objection. From your comments, it sounds like you think someone is telling PFC Maier that he's not allowed to have a MWT.

All he's been told is that he can't wear it on the boot and instead needs to wear it in the proscribed manner - around his neck.

The only person arguing about the rest of your statement is yourself.

I’m trying to see if there’s a regulation that states it’s not allowed or if he just doesn’t like it

As SFC (Join to see) said, you're not going to find a lot of things that "you're not allowed to do". Rather, things like uniform regulations are prescriptive regulations - you're not allowed to do otherwise unless specifically authorized.

So, you won't find anything in the regulation saying you can't wear a MWT on your boot .. just like you won't find anything in there about it being unauthorized to have a pink bunny shaped feather duster tied to your pocket.