May I just ask out of curiosity, why you want to do that? From my understanding about custom roms you just need to unlock the bootloader than follow the steps to install it, but don’t take my words wait for someone with 100% certain knowloedge about it.
Most likely that will be fine, especially as the LOS version should match the same base as iodé (6.x = LOS 22.2, 5.x = LOS 21, etc.). But of course if there are things not working you may need to go back to stock first.
Yes. You could even try ‘dirty flashing’ (i.e. don’t wipe or format user data. If all goes well, OS will boot with your existing user-installed apps still there. Worst case is LOS doesn’t boot and you have to reboot to recovery and do the format then.
My apologies - I did not realise your bootloader is currently locked. In that case, dirty flashing will not preserve your as unlocking the bootloader will already have removed them.
You should still be able to install LOS over the IodéOS installation with no problem.