Betelgeuse is eminently replaceable in-game, partly because FD made an error in assigning the star it's mass.
The problem to be overcome, as always when proposing changes to the galaxy, is mass balance. Here is how we understand the Stellar Forge works:
- The Galactic Seed creates a pattern of mass, from which stars are condensed.
- Known real-world stars are then placed in their correct positions. The mass of those stars is subtracted from the galactic mass.
- Any "leftover" mass not used up by the real-world stars is then used to generate procedurally-generated stars nearby.
So, the procedurally-generated galaxy depends on Betelgeuse being where it is, and having the mass it has. Delete or modify Betelgeuse, and you delete the procedurally-generated galaxy and replace it with one that is almost, but not quite, the same.
The only loophole that allows them to modify a star but kepp the rst of the galaxy as-is, is if the star being deleted is replaced with another one that has exactly the same mass. This is what they did with TRAPPIST-1, deleting a procedurally-generated star and replacing it with another star of exactly the same mass.
The good news is, FD made Betelgeuse way, way too lightweight. It's only got 0.2578 solar masses; the real Betelgeuse is about 400 times more massive than that. So it shouldn't be any trouble at all to delete Betelgeuse and replace it with a stellar remnant weighing 0.2578 solar masses.
The main "problem" will be the nebula, which an exploding Betelgeuse will certainly generate. Because, though they don't really look like it, nebulae in ED are "stars", from the Stellar Forge point of view. They have mass, which is subtracted from the background mass of the galaxy just like a star. I don't know if the Stellar Forge can handle the addition of a zero-mass object, and if it can't, then we can forget about adding a nebula around the Betelgeuse remnant.