I saw a photo of Michael Beck and Michael Pare on
agt_spooky's journal today and remembered the show Houston Knights (another buddy copy show -- this one set in Texas). And I remembered fanfic. Couldn't remember who wrote the series or any titles. I only knew that it was slash and had shape-shifting centaurs. Yeah, that bit I remembered. I found the stories with surprising ease with a Google search. The stories are on Gila's Cave as the Horses of Different Colors series by James and Wolfling.
I obviously have way too much time on my hands.