How do you know you're not similarly mistaken about wireheading?

I'm a bit skeptical of how well you can use the term "mistaken" when talking about technology that would allow us to modify our minds to an arbitrary degree. One could easily fathom a mind that (say) wants to be wireheaded for as long as the wireheading goes on, but ceases to want it the moment the wireheading stops. (I.e. both prefer their current state of wireheadedness/non-wireheadedness and wouldn't want to change it.) Can we really say that one of them is "mistaken", or wouldn't it be more accurate to say that they simply have different preferences?

EDIT: Expanded this to a top-level post.