They already covered the inside of it with Islamic graffiti.
But isn’t it still a Catholic Church?
I was there last year. One of the things that struck me was all the crosses in the church that they tried to obliterate when the muslims took over Constantinople... on the doors, the marble, the paintings... they’re vandalized, but you can still make them out.
The other thing that made an impression on me was that the Blue Mosque seems to be an identical copy of the Christian Haja Sophia Church. In fact most of the mosques that I saw in Istanbul had the same motif.
I found it strange that they would model mosques after a church.
One more thing, when they had the call to prayer with loudspeakers from the minarets, everybody seem to go on with their business - didn’t see anybody get down and pray.