OpAmp spice model that includes the Null Offset pins?
So, if you look at the datasheet of the TL072, on page 13 it shows where the offset pins attach.  What you are essentially doing when you do the recommended offset circuit (on page 12), is putting new resistors in parallel with the 1080Ω resistors.

The absolute most you could change this is going to be if you were to remove the 1080Ω resistor on one leg or the other by connecting that pin directly to V-, and then to attach the other to V+.  This would obviously be a little silly, but it would rail the output of the op amp.

I wouldn't recommend using any V+ voltage on the offset pins, but you can get a larger range in the zeroing by using a smaller pot, and a smaller tail resistor than the recommended circuit offers.

Hope this helps.  If you want more help, we are going to need more information about what you are doing.