Is there a possibility to use different chord symbol variants for the same type of chord? For example to use the crossed circle symbol for one half-diminished chord and “m7(b5)” for another half-diminished chord in the same flow?
Yes, though it’s a bit involved. If you edit one of the chord symbols a tiny bit (double-click it in Engrave mode, and make some minute adjustment to it, such as moving one of the components left or right a touch), then when you subsequently change the engraving options for chord symbols, those edited chord symbols won’t change in accordance with the options. If you subsequently do want to change the chord symbol so that it does follow the options, select it and choose Edit > Reset Appearance.