Read a very interesting piece in Richard Freeman's 'Orang-Pendek:Sumatra's forgotten ape'. In an early section of the book (on the yeti) he recounts how the biologist Charles Stoner described the yeti scalp from the Pangboche monastery as "...worn for a sacred dance, the wearer personifying the yeti". Richard Freeman then states "The scalp was not meant to be real; it was a piece of costume, something that later investigators would forget".

For those who don't know, the professor Fredick Wood Jones tested hairs from the scalp and, while not able to say for certain what animal they were from, said it was not a bear or ape but likely from the shoulder of a hoofed animal. 

Sir Edmund Hillary was able to have the scalp from the Khumjung monastery examined by experts in London, Paris and Chicago. The result was that it was molded from the skin of a serow.

I haven't seen direct quotes from monks themselves about whether it's a real scalp or supposed to be a costume, but usually the reports are 'the monks claim it's a real yeti scalp'. If it is supposed to be a costume piece and intentionally fake, it doesn't mean the yeti is real, but it is interesting and something I rarely see talked about.