BIABman:

You said: "You've just frozen the track.
Now you want to make more changes to it.
Do you unfreeze, change and then re-freeze?"

The answer is YES.

For changing your F note to an F#, it may be easier to go back to Piano Roll mode, then (as you've discovered), just grab the middle of the note bar and move it up.

Good luck!
LLOYD S