Thanks for your reply, Mark!
Definitely, software version control systems were not very established back then lol.
Unfortunately, I have tried what you suggested, but there are not easily identifiable tags within the file except for "BB3D" and "_BSP" at the beginning of the file.
Since the amount of lights won't be very big (it's a small game for a compo), I think I'll just write their position, color and radius manually on a separate file and use that.
Great to see that you are active and I am really looking forward to see your future projects (although I assume they won't be related to Blitz/Monkey!).