Do rappers pre write their freestyles?

Freestyle is a style of improvisation, with or without instrumental beats, in which lyrics are recited with no particular subject or structure and with no prior memorization.

Is it a freestyle if it’s written?

So it’s basically free of style, that’s really what a freestyle is. Off the top of the head, we just called that “off the dome”, when you don’t write it, just say whatever comes to mind. Really, a freestyle is a rhyme that you write that’s free of style.