This is a quick overview of all non-exposed registry keys VP parses.
(some might not work correctly anymore, who knows)

"Player" / "EnableLegacyMaximumPreRenderedFrames" always force old VP9.X-like hack to force the driver to discard pre-rendered frames
"Player" / "PhysicsMaxLoops"  if the table sets max loops to -1, then this will override it
"Player" / "GlobalDifficulty" overrides default slope/scatter/flipper difficulty of all tables (0..100, easy..difficult)
"Player" / "Autostart"        presses start after loading a table automatically
"Player" / "AutostartRetry"
"Player" / "asenable"         enable autostart? (0 or 1)
"Player" / "mirror"           mirror playfield (also mirrors keys accordingly) (0 or 1)
"Player" / "Exitconfirm"      seconds that escape key has to be pressed to exit VP completely
"Player" / "Volmod"           sets default sound mixer volume (0..1000)
"Player" / "PlungerFilter"    overrides plunger filter table setting ("Filter Mechanical Plunger")
"Player" / "PlungerNormalize" overrides plunger adjust table setting ("Mech-Plunger Adjust")
"Player" / "MinPhysLoopTime"  artificially lengthen the execution of the physics loop by X usecs, to give more opportunities to read changes from input(s) (mainly useful if vsync is enabled, too) (try values in the multiple 100s up to maximum 1000 range, in general: the more, the faster the CPU is, recommended tuning factor is 900 (90%))
"Player" / "BWRendering"      experimental fake Black&White rendering, which can be tremendously faster on tablets (0 (off) or 1 (better quality) or 2 (could be faster on some very slow/old devices)). Currently only works without dynamic AO and any kind of AA disabled
