So I've downloaded a 240% save and when I use the hex edit solution detailed in a post here, I get the message that it was created for a newer version of the game, is there a solution to this or did i hex edit incorrectly as I must admit that I've never really done anything like it before.

thanks in advance for any help

Silly question, but have u tried updating the game?,i had the same proble with the witcher 3[and still have] that it wouldn't let me use and older version of the game with a new save so i had to update and paste it again in the save files.
Maybe if u update both versions the Steam and GoG one [assuming you are using both] you can then move it to wherever u want.Dunno but it might be worth a try.