For 27909.1000 my workaround was add ServicingStack_26100.4651 & regedit settings manually, then go back to 27909.1000 when mod was done.
reconstructwindows.cpp cbsclient.cpp token.cpp hollowout.cpp glob.cpp bindings.cpp globals.cpp helpers.cpp hydration.cpp container.cpp extraction.cpp findcp.cpp repair.cpp cache.cpp commit.cpp query.cpp fusion.cpp parallelhydrator.cpp staging.cpp store.cpp verify.cpp scavenge.cpp query.cpp closure.cpp turbostackutil.cpp component.cpp install.cpp session.cpp hydrationrecipeparser.cpp store-version.cpp tlc.cpp cbsverifytrust.cpp cbsutil.cpp cbsfile.cpp iuutils.cpp pendingxmlparser.cpp file-sil.cpp reg-sil.cpp preload.cpp servicinghelper.cpp cbspackageparser.cpp xpgutil.cpp cixparser.cpp . . .
as for audio driver i think i figured it out too. audio on sl7 works from 1904x.1503 and above version of acxhdaudio.sys
touchpad - hidspicx.sys audio - acxhdaudio.sys these files come from cumulative updates hidspicx -> system32\drivers acxhdaudio -> system32\driverstore\filerepository and winsxs\amd64_dual_acxhdaudiop