SCP Foundation

You are taking a massive risk with this concept. Not only do you have a Thaumiel Class SCP that completely disables other SCPs who touch it, but you also have your SCP disabling SCP-173, one of, if not the best known SCP in and out of the site.

This isn't inherently wrong, but be aware that you are placing your first article on this site under an extreme amount of scrutiny.

In regards to the cross-link itself, I would advise against it. The reason is because most good cross-links enrich the article, but don't act like a pillar. That is, your SCP should be able to stand on its own whether or not the cross-linked SCP is present. I can't say that yours does this since half of your article is dedicated to your SCP disabling SCP-173.

I'm not going to advise you to turn away from the concept itself. I believe in execution above concept. I am, however, going to advise that you get rid of SCP-173 from your article and make what's entirely yours really shine and stand out first. Once your SCP can excel on its own, then cross-links in general, and maybe even 'risky cross-links' like this might serve a contributory role in your draft. As it is right now, I see SCP-173 taking away more than it gives.

SCP-X is to be assigned to a standard staff dormitory in Site-24. SCP-X is to be allowed to roam all Site-24 Level 1-2 locations. SCP-X is not to be found in any Level 3 or above area without being accompanied by personnel(s) with the appropriate clearance.

Remember, the Foundation is more like a prison than a hotel for nearly every humanoid SCP, and more like an asylum than a hotel for even the most special and cooperative of humanoid SCPs. Quite simply, the Foundation won't really allow anomalies to just wander around. To quote from the Humanoid SCP guide,

SCP objects should not be allowed out of their containment when not being transported, and should not be given access to other SCP objects, because that is a containment breach.

Now you mention that SCP-X has been given a staff dormitory instead of a containment cell so let's address how the situation changes as a result. As of right now, the situation doesn't change at all. In the long run, that depends on you because the burden of justification is now on you. Quite simply, you cannot just state that the Foundation employed SCP-X because it's useful; you have to justify exactly why the ultra-paranoid Foundation would consider letting this anomaly not only roam around, but also risk neutralization(death) by deploying it against other SCPs.

personnel(s)

Personnels isn't a word. Stick to personnel.

If SCP-X is to be found attempting to leave Site-24 without being accompanied by its assigned MTF squad, SCP-X is to be confined to its room for a period of no less than 24 hours, unless the need arises for SCP-X to be used.

This relates back to the earlier point about the Foundation not operating a hotel service. This entire section, from an in-universe perspective, would be rendered redundant if SCP-X was treated like any other humanoid SCP and kept in a cell. MTF units are highly trained, elite units and making them escorts is a bit of a waste. Remember, while the Foundation does have an interest in maintaining some amount of spirit in its sapient, humanoid entities, it is also an optimizing organization that will not waste money or material or manpower for a convenience.

SCP-X’s anomalous property only manifest when SCP-X comes within physical contact of an anomalous object, hereby classified “SCP-X-A”.

"Property" should be "properties." Coming within physical contact with something sounds a little off. I'd recommend saying "makes physical contact with." Classifying whichever anomalous object SCP-X contacts as SCP-X-A is…troublesome.

Usually, XXXX-A and XXXX-1 formatting is reserved for different iterations or creations of the primary SCP. SCP-X did not create SCP-X-A, and yet technically, one could argue otherwise. Personally, I would recommend using a different moniker for the affected anomalous object. Simply using 'affected/targeted object' can serve your purposes without getting knee-deep in naming conventions.

When SCP-X comes into physical contact with SCP-X-A, SCP-X-A will lose all anomalous properties for a time period proportional to the duration of the physical contact.

We will address this line in the concept check.

SCP-X is predicted to be able to use its anomalous properties an infinite amount of times.

There's nothing wrong with showing the Foundation's evolution of knowledge regarding SCPs. However, they are still statements that the Foundation would only ever make after utilizing the scientific method. That is, SCP-X had to have given the Foundation some indication, something seemingly concrete enough to be considered supporting evidence, that it could use its anomalous properties an infinite amount of times before this statement could be made.

SCP-X can only use its anomalous properties a limited amount of times proportional to the amount of time it has remained in physical contact with SCP-X-A.

I'm going to be honest, I don't really understand what you mean by length of time remained in physical contact. I imagine you mean that the longer SCP-X holds on to -A, the longer the nullification lasts. However, you go on to state that SCP-X will lose consciousness after 3-5 seconds of contact. This could be clarified better.

SCP-X appears to cease brain functions for this time, until approximately 5 minutes after contact is broken, when SCP-X awakens and brain function is resumed.

Brain functions ceasing completely for five minutes sounds pretty serious to me. I think even comatose patients have some degree of brain function keeping the heart beating and the breaths coming. I would either rework this or clarify that this is an anomalous property.

Currently, SCP-X is assigned to MTF-Upsilon-24 for Keter class re-containment, although SCP-X is expected to greatly resist deployment when the need for its abilities arises.

I have mixed feelings about this. The burden of justification is on you again for this matter. The primary question you should focus on when working with this statement is "why isn't SCP-X just used for every Keter ever?"

I'm not going to go over the discovery and addendum because they make up the half of the article that deals exclusively with 173. See the first collapsible for why.

In conclusion, I'm going to say this is an ambitious project. The 173 reference is a big issue and I recommend fleshing out your SCP first. That being said, I recommend remembering the Foundation is not a hotel when revising your containment procedures, and making your description crystal clear. But there's a line I said I'd address.

When SCP-X comes into physical contact with SCP-X-A, SCP-X-A will lose all anomalous properties for a time period proportional to the duration of the physical contact.

This is technically an overpowered SCP. This alone will be your single, greatest hurdle in working with this concept. Furthermore, I don't believe "it hurts when it turns off Keters" is a good enough cost for what SCP-X can do. That being said, I recommend bringing this SCP to the Brainstorming forums and specifically asking for advice as to how to keep or refine your SCP's concept without making it come across as overpowered. This forum will also help you in filling up all the page space that would appear if you get rid of the 173 reference. Good luck!