People should feel free to sing what they like. However, this being billed as a "launch of the CD set", punters coming for it may well have the reasonable expectation that they will hear at least some of the songs presented. That is the point of a launch after all - we cannot say to the audience "buy the CDs then you'll know", or "watch YouTube to find out". Still, if anyone would rather sing other songs than those that they sing on the CDs, nobody will make a fuss about it, I am sure.