As it happens, by way of example, our Bad Blood novels were written in third person then re-written into first person.

Crossover was written in past tense then re-written into present tense.

And in The Apocalypse Door, I alternate chapters in first person (past tense but set in the Now) with chapters written in third person (past tense but set in some twenty years earlier), and have them collide in the climax.