I'm not familiar with the specific amp, but I would assume that the answer is "no." Presumably the output transformer is designed such that the output tubes see essentially the same load when a 4 ohm speaker is connected to the 4 ohm tap as when an 8 ohm speaker is connected to the 8 ohm tap. Also, the bias current is DC, which won't be affected by what is on the secondary (output) side of the transformer since transformers can't pass DC between their two windings.
Regards,
-- Al
Regards,
-- Al