Does output transformer make a difference?

[teemuk]

I was reading about Mesa Boogie "Lonestar Special" amps and they can switchh from push pull to single ended with the flip of a switch somehow.

Switchable Single-Ended, Push-Pull Guitar Amp


These might be on topic as well:
Patent US8026765 - Audio frequency amplifier - Google Patents
Patent US7348845 - System and method for employing variable magnetic flux bias in an amplifier - Google Patents