TMZ broke the story ... Swift used the pseudonym for "This is What You Came For" to keep the focus on the song and not her relationship with Harris. But now that they've declared war on each other and the cat's out of the bag, the credit has officially changed.
Swift changed the name on BMI, which protects licenses for songwriters. Swift is now listed as a co-writer, along with Calvin.
It's unclear if the change is a prelude to a bigger, possibly legal fight.