Yes, you're right, it IS getting interesting. I can hardly wait to see how they are going to explain away the fact that Constantine changed the Sabbath from Saturday to SUNday. Constantine a 'man' changed one of God's Laws. Keep the Sabbath. Or how the Julian/Gregorian calendar changed the way days are reckoned, and changed when the new year begins.
An interesting tidbit:
Religious differences made several states retain the Julian calendar. Germany did not adopt the Gregorian until 1700, Great Britain until 1752, Russia until 1918.
Deuteronomy 12:32
32 What thing soever I command you, observe to do it: thou shalt not add thereto, nor diminish from it.