If you get the same brand and same type tube,you should be able to just install the new tubes...That's always been the theory behind Groove Tubes and their numbering system.
Even if you buy a bunch of non-matched tubes from the same supplier, you could see upwards of 15-20 mA range in tubes from the coldest to the hottest in the same tube model.
They get to sell their own tubes to the owners of their amps. They get you for the purchase price of the amp which comes with a warranty, and then get into your pocket for the maintenance.