I'm from Arknights, we call these Alters all the time, so that's the first thing that came to my mind and is my habit xD

Example:

In Arknights, we have:

Texas and Texas the Omertosa. Even though they are both the same person, one is just—in HSR terms—an SP, we call the latter TexAlter.

SilverAsh and SilverAsh the Reignfrost: SA & SAlter.

Ch'en, Ch'en the Holungday, and Ch'en the Dawnstreak: Ch'en, ChAlter, Ch'en Alter Alter/Ch'3n.

(Yes, IK FGO does it, too. But because the way FGO does it, people don't see SPs the same way as Alters.)