What if McNally's job was to deflate the balls to fit Tom's preferences --- within the range prescribed by the rules?
We have heard that the balls are often over-inflated, and that Tom's stated preference is for them to be on the lower end of the range.
So, couldn't McNally refer to himself, jokingly or otherwise, as "the deflator" in that context? Especially if Tom frequently makes a big deal out of the balls being prepared to his specifications, including making sure they are not overinflated?
That's a plausible explanation that doesn't involve rule-breaking.