Yep, HUCA works wonders in quite a few other fields too
And yep that's right; My question was whether someone could upgrade someone else's reward flight with their own miles, for example: Richard books a reward flight; Patrick upgrades Richard's reward flight using his (Patrick's) miles. This saves the miles transfer cost from Patrick->Richard. (I'm sure you knew the gist of it but just for clarity). Seems like it's a no for that.