No it is extreme of stupidity to mix high octane with regular fuel.
TURBO CHARGED ENGINES (CIVIC): If your car is turbo charged you need a fuel (RON 97) which cannot self ignite at high pressure. So you have to use high octane other wise regular fuel self ignite at high pressure (in tubo or super charged engines) which results in knocking. Pakistani people fails the state of art turbo technology by mixing the fuels and blaming the company for knocking. Even a small amount of regular fuel mixed with high octane can result in knocking. LESSON: you need pure high octane in turbocharged engines.
NATURALLY ASPIRATED ENGINES (CITY, BRV). These cars do not generate that much pressure which can result in self ignition. Engines are equipped with knocking sensors which regulate the head pressure and keep it below self ignition point of regular fuel (RON 91). However in these cars you car use high octane also without any problem. But this will be wastage of money without any benefit in driving. LESSON: Some companies allegedly use magnesium in fuel to increase the octane number. If this fake high octane is used in naturally aspirated engines magnesium residues can clog the catalytic converter very soon.