All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
There is nothing wrong with inviting the stated president to declare open the mosque because it is permissible, according to the preponderant opinion, to let the non-Muslim enter the mosque, except Al-Masjid Al-Haraam (i.e. the Sacred Mosque in Makkah), if there is a need or a benefit behind that; because the Prophet, sallallaahu ‘alayhi wa sallam, tied up Thumaamah ibn 'Uthaal Al-Hanafi in the mosque before Thumaamah embraced Islam. [Al-Bukhari and Muslim]
The author of Mughni Al-Muhtaaj (a Shaafi'i book) said: “It was proved that the Prophet, sallallaahu ‘alayhi wa sallam, let the non-Muslims enter his mosque. That was after Soorah At-Tawbah (Chapter 9) of the Noble Quran was sent down in 9 A.H. and the delegations came in 10 A.H. and among them the delegation of the Christians of Najiraan who were the first on whom he imposed Jizyah (tribute tax). He, sallallaahu ‘alayhi wa sallam, let them stay in his mosque and debated with them on the matter of the Messiah (Christ) and other matters.”
Allaah Knows best.