This has been bugging me for a while the way the drop down list of profiles to select from is very long!

The answer is to edit the text file called "options" located at /home/{username}/.config/RawTherapee

(you might need to enable "show hidden and backup files" to be able to view this directory)

There is a section in this file called "profiles" and you need to change UseBundledProfiles=true to UseBundledProfiles=false

ie

[Profiles]
Directory=profiles
UseBundledProfiles=false

When you restart Rawtherapee you will no longer see the long list of profiles as you will only see your own custom profiles.