I don't freeze tracks to often but when I do, I cant seem to make edits either once the track is frozen.
I believe this is because the synth is midi data and your frozen data is audio.
So what I will do instead is:
I will freeze a track, then create a blank
new Audio track. I will then hold CTRL + SHIFT while dragging the frozen data to this
new audio track What this does is it gives me a new copy of the frozen track to edit as I please, exc. while still retaining the frozen track for future edits if needed.
the reason to freeze a synth is to free up resources. as in all your edits are done and you like the way everything is, thus you want to freeze it to save on CPU. So you might want to get in the habit of doing edits first, then freezing the synth vs freezing it then doing edits.