well if we go back to your idea of the Tesseract as being a sentient female being, then that might be the answer, if that is the way they go. (we are here to speculate, after all) And then the Tesseract/Beyonder creature could change Algrim.
In any case, hmm... that's right, now how does Algrim change to Kurse without a character or other catalyst like that? and that could certainly be considered a brief short role, especially if...
I sort of prefer this idea about Hela at the moment but I think the above is possible too.
Again it seems such a waste to put her in a lot of makeup so she's unrecognizable for what seems like an unnecessary and brief role.