For some reason this limits the available accessories to 20, could do with overriding it and returning early if people want to add more accessories.

Jinxiewinxie and I had no problem allowing a player to use more accessories by bypassing this method entirely, unfortunately it is also called when the save file is loaded so it then defaults the player's chosen accessory to < 20. Overriding this method would be nice.

This wont be possible SMAPI, so I'll close this issue. I've opened one over on the Farmhand issue list :)
https://github.com/ClxS/Stardew-Farmhand/issues/34