We need to convert a multi select box to single select, and the option for doing this in the Change Field Form window looks scary.
Warning: This functionality is currently in beta stage. Consider backing up your database before using it. Click "Cancel" to return to the "edit custom field" form without making changes.
The option most suitable appears to be "Radio (not safe)". What does "not safe" mean? This field is a crucial element of our membership system and can't be at risk.