If you were to tie a single overhand after the larks head I doubt very much you would have any significant slipping. It also wouldn't add enough bulk to the knot to equal the bulk of two bowlines or sheet bends using two sheets. I do believe that it would fray the sheet over time as the the knot twists after changing tacks. But then, just the larks head would do the same thing as it slides back and forth.
I have a ketch with a staysail stay and all I do is cruise around. I never change headsails and use sheet bends on two sheets. Even with a marlin spike you will be hard pressed to get this knot undone.
I love being on an Even Keel WTF are YOU lookin at?????