There's usually not an option for PC to/from Core products from co-brand. Co-brand's can up/downgrade within their family but, IIRC USB doesn't really carry multiple versions of a co-brand like Chase, AMEX, etc.
USB has different versions of Korean Air Skypass, Aeromexico Club Premier, and LATAM cards. Product changes should be fine within those brands. Citi is the only one I know for sure will usually do a product change from/to a co-branded card and a core card (like Diamond Preferred to AAdvantage Executive, which they offered me when the Prestige card disappeared for a while last year).
Out of what seems to be 1000's of cards / families it's hard to keep track of all of them. Generally though.... When in doubt ask the issuer?