In the tagging program Mp3Tag it's possible make presets which eg: add text to the beginning or end of a tag field, change underscores into spaces, remove double spaces etc.
I would love the option to select one or multiple tracks and apply such custom presets. Probably easiest would be right clicking the selection and then have a drop-down field called action with all custom tagging presets inside. Or even better, an actions button directly on top of the musicbee interface as it is in Mp3Tag.