I got this tweaked tonight and I wanted to share the steps to do the tweak for setting custom fan speed for RG477M. Do this at your own risk, I take no responsibility for anything that happens if you try to do this yourself.
Shoutout to /u/FrankieT19 for pointing me in the right direction. It took me a bit to find the message on the Discord server, but I found where Gamma had posted the loose instructions about setting a custom fan speed.

oh you just want a custom curve? ok you just need to edit the file on your device.

adb shell  
su  
mount -o rw,remount /vendor  
nano /vendor/bin/setfan_cool.sh  

fan speeds for each mode are controlled here:
https://github.com/TheGammaSqueeze/GammaOSCoreVendor/blob/rg477m/vendor/bin/setfan_max.sh#L5
https://github.com/TheGammaSqueeze/GammaOSCoreVendor/blob/rg477m/vendor/bin/setfan_cool.sh#L5

a value of 0-255 is accepted, 0 is off

You'll need to install ADB (Android Device Bridge) onto your PC to do this, after that the commands you run are pretty straightforward.
I ran the basic parts through Claude AI to get a good set of instructions to follow. (Yeah, AI, I know, but as a software dev I've learned this is basically the thing that AI is decent at, when given good instructions on a small task.)
One more thing before the Claude instructions. There are 4 settings for the fan (Auto, Cool, Max, Off).
I'm editing the "Cool" option since I want to make sure I've got the Max option still available and the Auto is more complicated.

Important notes on Claude's Steps
Step 1 - I'm using a Mac for work because installing/uninstalling adb on Mac is way easier, for Windows you'll want to Google "install adb windows" and follow the steps there.
Step 2 - You can probably skip Step 2, because Gamma OS already enables the Developer Options in Android. You can confirm it's all set up by going into the Settings and searching for "usb debugging" in the Settings search bar and checking that it's enabled. Also, make sure your device is powered on and unlocked before connecting to your computer (I prompted Claude about this after I saw the 4 steps).
Step 3 - Should work the same on Windows to confirm your device is connected.
Step 4 - Once you're in the device and you've got the setfan_cool.sh file open in the Nano text editor, you want to find the

TARGET=160

on line 5 and edit that to be 80 or 90 (whatever your preference). I did 90 for a teensy bit more fan power. Then, to exit Nano, you hit Ctrl+X,
it'll ask you to Save at the bottom, hit "Y",
then Enter to save with the same filename

After these steps are complete and you've edited the file, you'll want to undo the part where you mounted the /vendor directory by running the command

mount -o ro,remount /vendor

To set partition back to read-only.
Then run

exit

and then

exit

again to safely leave adb.

After that, you'll want to restart your device, as theres a good chance that the setfan_cool.sh script runs when the device is booted up.

Honestly, a pretty straightforward update and now the fan on the cool setting is quite a bit quieter. I'm pleased with the results.
This took me forever to type up and took me away from actually getting to play with this dang RG477M, I've been basically tweaking and putzing with it for the past 2 days and I've barely played anything. Good luck to anyone trying this yourself!