Hello!
If I have standard Asus Firmware and want to try Merlin can I then keep the settings, or at least upload the settings file. Or do I have to add all settings again manually?
When you change firmware versions/forks you should always consider a factory reset and re-enter your user settings - but you can also use John's User NVRAM Save/Restore Utility to do the job for you!
You should not save/restore settings with the firmware internal function as it does also save the hidden (firmware specific) setting which should be reset after the firmware update - only the user entered settings should be restored!