Mod X has a custom global variable that gets referenced as a property in a quest script. However, for compatibility with DLC, that quest script needs to be modified. Without altering the original Mod X, how is it possible to create a patch that references the custom global variable without turning it into a null reference?

I created the original mod in the CK.

I open the original mod as an inactive file along with the DLC I need to be compatible with (Dragonborn).

I open the quest that needs editing and I change the script. I make sure all the properties point to the right targets, save, and close.

When I reopen the file (which is apparently not requesting the original mod as a master) and check the properties, the custom global value being referenced now says "NULL form". I can clear the value to <> and then auto-fill it back to the correct reference, save, close, and repeat and every time it winds up back as null.

What am I doing wrong?