As a clarification, if one’s personal Rav were to theoretically give a psak that it’s mutar to ascend parts of Har Habayis, then the person hasn’t done an issur.
Regardless of contemporary Gedolims’ position to prohibit ascending any part of Har Habayis, the da’as yachid is legitimate as long as it follows the halachic process.
In Yiddishkeit, we don’t have the halachic equivalent of a “Pope” to heed. Torah lo ba’shamayim hi.
(I am nevertheless NOT advocating ascending Har Habayis).