The Feast of the Theophany

Today is the Feast of the Baptism of the Lord in the Roman Catholic church. In Orthodox churches, this event is celebrated on January 6th, when we have our Epiphany celebrations of the magi finding the Christ child, and is called the Feast of the Theophany because it was at the Baptism that the three persons of the Trinity were manifested.

I wonder if it is kosher to borrow feast days from a church one is not a member of (or to use the work "kosher" when talking about Roman Catholicism and Eastern Orthodoxy). It doesn't make much difference now, being as the Feast of the Theophany has passed. Perhaps next year. For now, we await the feast of Saint Theophanes, which falls on quite the coincidental date, given I didn't know the fellow existed when I named this blog (only my close friends an family will understand the connection). There are no coincidences.