I'm a bit surprised by your claim that the neck bore didn't change. Where does your information come from?
Here is a much more reliable technical summary:

Selmer Supreme Tenor Saxophone - Sax.co.uk
After 8 years of secret development, Selmer Paris reveal to us their ‘best tenor saxophone ever designed’ After 100 years of innovation, design, and manufacturing of the saxophone, Henri SELMER Paris redefines the modern identity of the tenor saxophone with the SUPREME.

and they mention a bore modification for the neck.
So, the new Supreme tenor neck can probably not be retrofitted to an older model --for the alto, they are selling the Supreme neck separately as an improvement.