I already have the standard edition and I would like to buy the supercharged version, but I can’t actually do this without buying the whole game again. Is there any way of just paying $10 for the uprgrade and it then updates your game to that version?
Thanks 
Heyya!
From the FAQ:
Unfortunately this is not possible at the moment as there are too many logistical complications and transaction fees involved which make this bad business for us.
Once we are on Steam though that changes and it will most likely be possible to at least get the V16s and other new engine types (after the full release) as DLC.
how far are you guys off coming to steam im waiting to buy the game . so are alot of my mates say at least 7 of us . just a idea would be nice so i can let them all know hopefully its soon
They are already Greenlit. Thats what I know.
Steam looks to be happening for us in late spring right now. We definitely need to get some polishing done before we will put it on Early Access
thanks for the quick response they will be real happy its coming before xmas .be a good bday present for my self cant wait to make a ls1