Note: Microsoft GS Wavetable Synth (or at least the one I have on my Windows 8.1 computer) does respond to a
GS Reset (F0 41 10 42 12 40 00 7F 00 41 F7) to
enable some GS banks.
It also interprets any of the following GM messages as "reset back to General MIDI Level 1":
GM1 System On (F0 7E 7F 09 01 F7)
GM System Off (F0 7E 7F 09 02 F7)
GM2 System On (F0 7E 7F 09 03 F7)
In fact, the Microsoft GS Wavetable Synth appears to let you turn on the GS mode with F0 41 xx 42 12 40 00 7F 00 xx F7, and return to the General MIDI mode with F0 7E xx 09 xx F7, where each of the xx bytes can be anything. Of course, it's a good idea to stick with the official GS Reset and GM1 System On messages shown above to ensure compatibility with other devices.