I think wearing an affiliated tartan you aren't affiliated with is ok as long as you show some respect to it. My only two tartan kilts now, only one is a "real" tartan and it's black watch and I have a lot of respect for them and their history. my next will be a Morgan tartan. I am not a Morgan, but a high school teacher I had was, and he was very much like a father to me, so much so I took his last name as my middle name. so I asked him if I could wear the Morgan tartan, mostly as respect to him. he was honored and I will be as well when I put it on and send him a picture. tartans are about clans, family, and connection. it doesn't have to be blood. the bond can be in spirit as well.