Unfortunately I think part of it is just experience, when it comes to switching out yarns. I am with you though, i hate the fact that these patterns tend to be one yarn only!
With respect to the yarn that you got and you arent sure about.....if you really dont think you like it, either send it back or ebay it. Life is too short to hang on to mistakes. Last night I was looking through my stash, and I have several "what was I thinking" purchases....I plan on doing a major ebay sale of both yarn and fabric in the next few weeks....stop feeling guilty about buying a boo boo....and the stuff that can't be sold? Well, I gonna donate it darn it!!!