tung sol 6v6 with rebel 20 tube mix

Thinking of swapping the stock JJ 6V6 in my Rebel 20 for Tung Sol, I understand they are a little fuller. However, since Egnater likely had to design the amp to accommodate both the 6V6s and EL84s (i.e. neither may be optimized but a reasonable tradeoff was found so both sound pretty good), I'm wondering if I may be upsetting this "balance" by introducing a power tube with slightly different specs. I know a lot of people have done it, but want to know if it is a good idea at a design level.

thanks