We know the things are customizable since Cait's has a knot and nubs and I imagine that it's something that could be done mechanically since the game has to track its length if nothing else. Maybe some future expansion could have you approach Evergreen about changing it. That said I don't know how the game actually tracks the player's ghostlight, so it could be trickier than I think. Probably not the highest of priorities right now either way.I'd really like to be able to customize the ghostlight piercing & add ghost balls alongside it, I know I could just get the real thing but I just like the ghost aesthetic more.
We've never seen one with balls so even if the devs do allow for future customizaiton I think that might be asking for too much complexity to be added to what was intended mainly to unlock content requiring a penis for players who otherwise want to play a fully female Champ. Though there are some bespoke scenes starting to get written that specifically account for the nature of ghostlights.