Baking – looking for a substitute for liquor in a cake recipe

On first blush, you will probably want a fat or oil with similar qualities as the "vegetable" oil you're replacing, such as olive oil. Butter has a much lower a smoke point, however, cornbread recipes exist that use butter or lard. I'd be willing to experiment, particularly if you're used to cooking with butter. (Just be careful with heat.) As far as quantity, I'd use a bit less than 1/3 of a cup, but that's me being defensive as I don't know the recipe you're using.

In the US, to be labeled as margarine, the product must contain 80% fat per the Standard of Identity. The spread simply cannot be called margarine.

However, with a fat content of 70%, it is quite close to a standard margarine, and is likely otherwise the same thing.

Almost all recipes have enough tolerance that you could substitute regular margarine, real butter, or another vegetable oil 1:1. If you want to be more exact, you could approximate pretty closely (for easier math) by just using 3/4 the amount of a 100% fat product like shortening or vegetable oil, or 7/8 as much margarine or butter.