ABB = Amperex Bugle Boy?
It's correct that rolling the 12AX7s will create a significant change in sonics.
According to the specs of your amp, the 12AT7's are the drivers for the power tubes. They increase the voltage from the preamp to the power tubes while also inverting phase. Rolling these tubes does have an audible effect on sonics, but the preamp stage will have a major impact on sonic signature.
Start with the 12AX's, then you can tweak the sound by rolling the AT's.
It's correct that rolling the 12AX7s will create a significant change in sonics.
According to the specs of your amp, the 12AT7's are the drivers for the power tubes. They increase the voltage from the preamp to the power tubes while also inverting phase. Rolling these tubes does have an audible effect on sonics, but the preamp stage will have a major impact on sonic signature.
Start with the 12AX's, then you can tweak the sound by rolling the AT's.