I doubt that there will be a firmware fix, as it was mentioned, that only older firmware versions had this issue. So the latest ones should not have this radio station issue. Fix for Mazda: Install new CMUs to the people - and they usually come from factory with the latest FW version, which should not have the radio station bug of the old FW included.
And FW 74.00.310NA is brand new. It was not available since last year. The post #239 you refer to, was updated just recently and the links were updated.