Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Open Magic Bullet Looks...
VP_MAGICBULLETLOOKS_LOOKSBUILDERParameter: Preview
VP_MAGICBULLETLOOKS_PREVIEWAFTERParameter: Mix
VP_MAGICBULLETLOOKS_STRENGTHParameter: Save Preview
VP_MAGICBULLETLOOKS_SAVEPREVIEW