Music
can I edit an iTunes song that I purchased from iTunes in Garage band and then assign the clip as a ring tone or an alert for a specific contact?
iPhone SE, iOS 14
I believe you can. See the 'Share a GarageBand song as a ringtone or text tone' section in.
Share songs with GarageBand for iPhone - Apple Support
FWIW, there are many (free) apps in the App Store that will convert a song in your music library (that isn't DRM copy protected) to a ring tone without using GargaeBand.