Is it permissible to pray Istikhara to choose a mandatory legal ruling when there is a difference of opinion between two views, in order to know which of the two views I should act upon?

If one side of a difference of opinion in a matter becomes preponderant, either by asking scholars or by examining the evidence for those qualified to do so, then it is obligatory to follow it. If no preponderant side becomes apparent and one of the two sides is closer to caution, then it is better to follow it, due to the Prophet's (peace be upon him) saying: "Leave what makes you doubt for what does not make you doubt." If both matters are equal and neither is closer to piety, then seek guidance from Allah and take what your heart feels at ease with.