This is true, in that my thesis was about what I called "cross-level planning" and the phrase was indeed repeated many times. However, it's false in that the reason I abbreviated it to "XL" wasn't that it was repeated so often. Rather, it was because the thesis was over the word limit and I needed to cut back as much as I could. Abbreviating "cross-level planning" to "XLplanning" saved me two words every time.
Rather ironically, in my viva voce I was told that the PhD would be awarded if I made a single modification: remove an entire chapter.
Needless to say, I didn't use the opportunity to change all occurrences of "XL" back to "cross-level"...