Linking accounts is good, I know some do put their CO number for CO metals and UA MP# to UA metals to increase their shots at upgrades. However, according UA insider's post recently "mileage plus on tips and upgrade..." and one of her links, it's deemed not necessary to use different frequent flyer #, because PLT & 1K clear at the same time on CO metals.
http://www.mileageplusmergerupdates..../EliteUpgrades
So OP should be fine. ^