Don't know where the "high nitrogen" cut off might be, but anyy lawn fertilizer (without weed killer or insecticide) would certainly be high in nitrogen. Remember, nitrogen is represented by the first number in the three number group.
Example: 30-0-5.

Excessive nitrogen can sometimes make variegation less variegated. The white in green and white leaves might turn a bit chartruese, and the yellows might be on the green side also. I wouldn't use more than a tablespoon of lawn fertilizer per plant per year.

What ever you deside to use, follow the directions on the packaging carefully, more is not always better, more can be harmful. I have accidentally burned plants this time of year, it is disappointing because you are trying to do a good thing. I have found that diligent use of miracle grow or other 10-10-10 provides very nice results.

Good luck, Helen.