He wasn't changing accepted Christian practice, just recognizing it formally as the representive of the Roman state.
Don't you think, if the celebration of Pascha had been unknown and everyone worshipped on Saturday, we'd have some record of complaint or protest when those things were changed by a government which had only recently stopped being a persecutor?
By 100 AD Passover and Sabbath worship was still being practiced by the Church. Indeed there were some, as the Apostle indicated in 1 Timothy 3 , that were already teaching a different doctrine... well before 100 AD.
Both Easter and Sunday worship were being practiced by AD 100.
Campion, this statement is very telling. Some of us are trying to worship in the spirit and the truth of the early first century Christians.