How can I easily change the size of the accidental in a chord symbol ie. F#7 to make that accidental larger without also making the other altered accidentals larger in a chord like F#7(#9#5)? I can’t seem to find the font style that only alters the scale degree accidental component of a chord symbol.
The scale factor for the accidentals in the alterations is determined by options in the Design section of the Chord Symbols page of Engraving Options.
If you want to change the size of the root accidental without affecting anything else, I think the way to do it is probably to use Library > Chord Symbols and add (say) F# as a chord symbol. Then select the # component, and click the little pencil icon to edit it: set the X and Y Scale values as you like, e.g. to 110%, then confirm the dialogs. Now any root # accidental will use your revised, enlarged sharp.