Does the reward for one who prays the two rak'ahs of Sunnat al-Tahiyyah and Sunnat al-Fajr with a single intention equal the reward for one who prays each of them separately?

The fundamental principle is that an abundance of effort and hardship in work increases the reward, as indicated by scriptural texts. Nevertheless, if there is a specific text or established Sunnah for a particular action, then adhering solely to what has been transmitted is better and carries a greater reward. Therefore, whoever enters the mosque after the Fajr adhan should limit themselves to the two rak'ahs of Fajr, intending them as the Sunnah of Fajr and تحية المسجد (greeting the mosque). Indeed, some few actions may be superior to many, because they are what is known to have been performed by the Prophet, peace and blessings be upon him.