What is "tube rolling" and can I do it with your amps?
Tube rolling is swapping out a different brand or sometimes a different model tube with close enough characteristics that it still works in the amp, but might sound slightly different.
Tubes have a part number that usually includes letters and numbers, such as EL34 or 12AT7. You can use any brand of tube with that same part number. There are a handful of companies producing new tubes today, such as JJ, New Sensor Corp, and a few others. Alternatively, you can buy "new old stock" or NOS tubes, which is a tube made at some point in the past by companies that may no longer be in operation, and the tubes were kept in storage and never used, and are now being sold. Some historically made tubes can be very valuable, depending on the brand, just like anything of high quality vintage nature. You might also find some used vintage tubes that are still in good condition.
Some tubes made with different techniques and having different part numbers can also be substituted for one another because the pin arrangements and characteristics are similar. For example a 6L6GC and EL34 tube can generally be substituted for one another. Others cannot be substituted and could cause damage to the tube or amplifier if used in the wrong circuit. Many tubes use similar sockets, but just because the tube fits, does not mean it can be used!
You can "tube roll" with my amps if you like. How different will the sound be when using different tubes? That depends. Like anything, different manufacturers might use different processes and materials and there is some natural variance in every tube anyway, even from the same brand. No two tubes are perfectly identical. But you generally shouldn't expect it to sound dramatically different. The selection of tube type itself, design of the circuit, and other components like the transformers will shape the performance of the amplifier overall, and rolling tubes is an additional variation on top of those other important elements. I tend to think it's a rather expensive form of experimentation, since a pair of good NOS tubes could easily cost hundreds of dollars, but if it brings you pleasure to try out different tubes, by all means go for it!