Has anyone here been able to change tuition rate from international to domestic after PR approval while the semester is still going on?
Depends on your school. Check with them what their policy is.
I did, and in my case I got a refund worth 1/2 the differential for international students. I know some institutions would not do that and will just adjust your tuition for the following term.
Again it depends on your school so you will have to check directly. Usually this policy is outlined, and should be, somewhere in the webpage.
I'd suggest connect with the people in the International Students office, they should know this.