You can get away with saying anything if you preface it with "Arguably," but if some other state had decided to opt out of the country during the Mexican War when Lee was fighting there, they wouldn't want to be around when he got back.
The Federal blueprint (Constitution) was beautifully designed; but that did not alter original commitments to a developing Virginia, which was for a long time the leading member of that Federation.
So Lee was loyal to his oath so long as Virginia was the leading state in the country? Doesn't say much for the guy.
I was looking forward to your explanation as to how this was a correct and proper method of interpreting Kansas Constitution Article 1.