Quidquid latine dictum sit altum videtur
The ability of Sneak Attack takes precedence here. But it has nothing to do with a general priority of plots over titles.
The ability of Sneak Attack is as follows:
Sneak Attack wrote:
You cannot initiate more than 1 challenge during the challenges phase.
The decisive word here is "cannot". Cannot is a teechnical term in AGoT - it denotes an prohibition that is absolute and can't be overridden by any means. This is covered in the Rules Reference, page 4:
Rules Reference page 4 wrote:
The word “cannot” is absolute, and cannot be countermanded by other abilities.