Below is my Fine Tuning screenshot for the MyMusic program based on my audiogram.
If you click on the CR button in the middle, it’ll show the 2 rows of compression ratios between Loud/Moderate/Soft. I find that I’m able to click up or down on a particular gain spot, and if I click enough time up or down, it may change the gain on the adjacent gain spots, either before or after it, and sometimes even the gain spots of the other rows. For example, clicking too much on the a Loud gain eventually may change the Moderate and Soft gains of that channel as well. It may also change the compression ratio displayed as well.
I haven’t found an occasion where I’m not allowed to change the gain value because the CR values are fixed. But if I keep on going, for example, keep on click up on the gain, eventually it’ll stop when it hits the max value it can sustain, and the bright red turns dark red on that gain spot and stops there. Conversely, I can keep clicking down on a gain spot until it even passes 0 and goes into negative value gains until it also eventually stops.
So I’m not sure why you’re locked out and can’t adjust the gain. The CRs are not locked up in my case. I wonder if you hit some kind of max value already in your prescription. Just as an exercise, pick any other gain spot and try to up or down its gain and observe what happens. After your experiment, you can just delete that MyMusic program and reinstall it and it’ll be all fresh again.