Unfortunately it's not possible, i've tried and works, but will break some things in gallery app like media scanning.
You can disable the stock camera app if you want, just go to settings --> app --> show all apps --> check "show system app" --> Camera --> disable the app. In this way you will have only GCam in your launcher
Yes, can be rooted without problems (i'm actually using Magisk because root helps me in development/debugging) and it's stable, but i did not understood the CPU throttling part, could you please explain? I'm sorry but i'm not following LOS development, they are using a completely different kernel/proprietary blobs, and there's no public work on lineage 19 for our device
PS: i've rebased and updated the kernel, i'm testing it right now and will include everything in next public release if it's 100% stable, if someone wants to give it a try here's the flashable zip download link:
https://www.androidfilehost.com/?fid=14655340768118455299
Sources are here:
https://github.com/B--B/Gemini-B--B-Kernel/tree/twelve-4.4-new
There are various improvements and fixes, also a couple of bugs spotted compiling the kernel with clang 14 has been fixed now, but as i said it's still in testing phase, if someone wants to give it a try please let me know how works and if there are regressions/bugs. Thanks