Technically one could achieve this through a cascade of console commands calling different script functions. However, that would be very tedious and complex. Regarding your problem: If a variable does not exist in the scripts, creating it won't make a difference, because the scripts obviously have no reference to it (otherwise the variable would exist). By any chance, do you mean that the variable exists, but is just "empty"? Then you should be able to fill it with the desired value using the commands listed above.

I'd like to add a new variable that does not exist in the Gothic, is there any solution how I can achieve that? The reason why I'm asking is that the current save I have, "DIA_GRAHAM_BUYMAPS" value is missing, causing the problem where I can't buy a map from Graham. Any thoughts?

@anonymous2306 This requires insights into the workings of the particular quest. As the description indicates, "the problem may only be fixed with clear instructions from the mod developers for a temporary solution."

How do I close a quest? The command on the WoG website doesn't work.