[itsme]

Using one of the user defined non group fields Custom / Custom2 as proposed is imho the way to go.
It is already available, including the possibility to sort by Custom / Custom2.
Useful improvements would be:
- allowing to rename the (non group) user fields, like it is the case for the user defined group
- adding more user defined fields and/or user defined groups
- adding a way to allow fast and convenient switching between several title format / caption format settings
Thus it would improve MSP also for users (like me) that do not number their songs. They could use the additional fields flexibly for other purposes.