errr.... i used to work in music copyright.
Under UK law, copyright expires 70 years after the piece is written.
You can't "extend" this (at least in the UK - or at least, you couldn't)
What is even lamer is that you just need a preforming rights licence and you should be able to play or perform any song on the premises. The _only_ way that this would not be allowed is if the owners of the piece have deliberately asked to be excluded from the performing rights license and have their own charging scheme for usage.
Seems somewhat stupid as the license royalties usually get distributed via sample percentages, which theoretically would mean that "Happy Birthday" has a very large chance of being in the sample and would generate shite loads of money.