and your UK-issued JAA license is replaced with an EASA license, the license number might change
As the licence will continue to be issued Nationally and not by EASA, this is unlikely however, for 11 years App 1 to JAR-FCL 1.075 has stated:
Requirements
III Licence number Licence number will always commence with the
U.N. country code of the State of licence issue.
The UK has never adopted this.