Nope, hats/scarfs you already have are not marked in any way and you and get same again. I guess for hats it could be shown if you've already got it but not really possible for scarfs as their lengths for example are random floating point values ie. never going to be the same.
Yea I guess I should point out on the descriptions that those are temporary. The gem addition ones do say if they're permanent or temporary but didn't even think about mentioning for paths as they're all temporary.