I use a custom field to select people traveling. It was set up as single select because I had not anticipated needing to select more than one person. However, today, I had that need but I cannot change the field type.
Just allowing a simple change to the field type would be so much easier than deleting and recreating the field. I really hope this ability is added in the near future. I often have project needs change in the middle of the project.
My temporary fix was adding a new single entry including both people. However, this is not ideal.