Hover the mouse cursor over the "Update flight controller in real time" to get some help text. It is a safety feature to not allow GCS to save settings while the vehicle is armed. Writing flash (settings) takes some time away from the stabilization task. Changing the settings as described above (moving the sliders, but not pressing Save) works but is not permanent. Trying to save the changes does not work. Maybe that is what you need. If you want to save settings, you can save them later after you land and disarm.
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Also; if I understand what you are trying to do, LibrePilot has
Stabilization "Settings Bank" 1, 2, and 3
(disarmed) Assuming you are using the default of Bank #1, go to the Stabilization page, click the flower next to "Settings Bank 2" and select "Copy" then "from 1". That will make bank 2 look exactly like bank 1. (maybe save settings here)
Then:
- click on the bank 2 tab to access the bank 2 settings
- change Bank 2 however you like
- save settings
- go to Input -> Flight Mode Switch Settings
- make one of your flight mode switch positions use bank 2 to use the different settings when you use that position
- save settings
- arm and fly
A problem with this is that most transmitter switches have at most 3 positions. You can actually buy rotary switches with many positions for some transmitters. The way most people get more positions is to configure the RC transmitter to use multiple switches on a single channel.
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Another way is to use TxPID which can change PIDs, roll rates, and attitude max bank angles as I recall.
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For Rate mode responsiveness or Attitude mode max bank angle, you can also simply configure a "dual rate" switch on your RC transmitter. Beware that arming using sticks probably won't work if you have clicked your dual rate switch to low rate on a stick that must go all the way over to arm / disarm.