A more easily reversible mod would be using half the power tubes. It's not as simple as pulling out one set, I think some resistors have to be changed as well, something like that, proceeed only with highly capable tech support....
English rockers used to do it with 100w Marshall scream machines to turn them into 50w Marshall scream machines. If they did that with one 12 instead of 4 it would have been quite effective.