You can use the WebUI for 95% of what is needed on an ARK server without ever needing to use ExpertSettings.
So do all that stuff first. Save, then restart. Just to make sure it all works fine.
The go to the Engine Settings page on the WebUI, scroll all the way down. See the blank area. Copy all your GAME.ini code there. Yes, ALL of it. I have lines after lines. Save, then restart.
Check the server again just to make sure. Then add your mod IDs in the mod page string. Add 2-4 at a time, save, restart. keep doing that until you have all mods in.
With each restart check the server first.
If you need to add code to the gus.ini, you have 2 choices.
(1) Use FTP and add it there. Note: make sure the server is offline for at least 5m. *OR
(2) use the file manager in the webui. You can open the file there, edit, save and restart.
Once you have all that you need in place, go to the Configuration Profiles section, save it. Use like a name. Example: As_Built_01132022.
Ftp and make a full backup to my PC. I do this weekly though.
Nitrado Support does advise everything above I suggest and to have the server offline.
I can basically roll back to any save within 15minutes, and even can rollback profiles as needed. I do this for each server, and for any clusters.
Not once I use the expert mode any of this. I don't because I am lazy and like gui's. Also when you grant admins permissions to your account, you can grant access to the webUI, and not the expert areas where I personally feel more accidents may happen
This is all just by personal experience and opinion.