Thanks so much for responding! I do agree that the twist feels forced, and you put it in a very clear way. But I still want to see if I can use it if I develop it more or alter its stakes.
I'd like to clarify why this deal was made, which I think wasn't addressed clearly in my short summary. The Foundation still feels as if it can contain the SCP, just with more research and time (as it turns out, they were wrong). However, as the spread of the SCP grows, and affected televisions grow more widespread, more unpreventable deaths are still occurring. The Foundation not only wants to minimize those short-term deaths, but it also wants to avoid a Broken Masquerade scenario that would surely come from a bunch of anomalous deaths. That's why they've been backed in a corner to stall the SCP with a 100-year period, they want to save lives and protect normalcy.
The SCP, on the other hand, also has a reason to make the deal. In its current state, the SCP can surely infect the whole world, but it's estimated that it can only do so slowly (I said by the 23rd century). This is because of what I mentioned, this SCP transfers slowly through non-electronic media, making it hard for the SCP to infect rural or non-industrialized regions of the world (I should also mention the more "digital" a medium is, the faster it spreads, hence the internet would spread it much faster than TV). For this aspiring "celebrity," accomplishing fame fast is a top priority. This SCP believes negotiating with this powerful organization can get him to stardom faster, without the hassle.
If the deal still feels too far-fetched, then I might just scrap it from here. But I don't think this is the primary issue with the twist.
Could the issue of stakes be solved if, say, the neurological impact of the SCP was altered from neural decay to neurological compulsion? Instead of the world dying, humanity would lose its sense of rationality by being so obsessed with the SCP's nonsensical songs. It would be more fitting of the SCP's "celebrity" construct I guess, and I can even take a stab at social commentary and how technology affects the mind.
Or maybe if the scope was smaller? I could make it so it only spreads through electronic information, thus primitive areas of the world will remain unaffected, giving the Foundation a last resort in case everything goes completely wrong.
I really don't want to play with the SCP's invulnerability, since it would ruin the danger. However, I could change the ending by saying that the SCP has been mostly eradicated by the internet, aside from a few dark-web sites that the Foundation can't find. It still slowly edits information across the surface web that stimulates curiosity for the "celebrity" (building a new fanbase), infecting more viewers that dig into the dark web. In making the internet, the Foundation has accidentally made the SCP uncontainable.
For this SCP, I based the high-stakes approach off of SCP-3002, who threatened the entire world's consciousness with an MK-class scenario. SCP-3002 was too powerful to resist anti-memes, becoming virtually invincible, yet I didn't find that approach to be artificial but rather just an ability of the SCP. I know it's hard to define what makes risk feel forced, but I guess I'm just scrambling for ideas, how do I emulate stakes like that of other K-class scenario SCPs without sounding contrived?