All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
In Al-Haraam Mosque, you can pray as many Nawaafil (supererogatory/optional prayers) as you wish during the times in which praying Nawaafil is forbidden in other places. The evidence for this ruling is the two following Ahadeeth.
Ahmad, Al-Bayhaqi, Ad-Daaraqutni, Ibn Hibbaan and Ibn Khuzaymah reported that Abu Tharr took the ring of the Kaaba gate and said: “I heard the Prophet saying: “No prayer is to be performed after ‘Asr until the sun sets, nor after Fajr until the sun rises except in Makkah, except in Makkah.” Al-Albaani mentioned this Hadeeth in his book As-Silsilah As-Saheehah. The second evidence is the Hadeeth reported by Al-Bayhaqi and Ibn Abu Shaybah from ‘Abdullah Ibn Babah who said: “I saw Abu Ad-Dardaa’ circumambulating around the Ka’bah after ‘Asr then prayed two Rak'ahs. Some people mentioned that to him, and he replied: “It (Ka’bah) is not similar to other places.”
This is the Shaafi'i opinion. But the majority of scholars are of the opinion that the ruling concerning Al-Haraam Mosque as regards Nawaafil prayers is the same as that of other mosques.
Allah knows best.