General

do you want raven horn cape for looks or bfc?

put raven horn cape as apperence and function as BFC = your BFC now look like lv140 empress cape ( the stats of BFC remind stays but looks will change)

or

put BFC as apperence and function as raven horn cape = your lv140 cape look like BFC ( same above but opposite)

edit: i got ninje'd by butterfly gurl >.<

Yes, but:
Raven cape ~> looks like bfc = set effect still
Bfc ~> looks like raven cape = [i]no set effect[/i]

The item doesn't change, just the appearance of it.

Yes, you can