yes and yes.higher octane burns slower to prevent detonation.if its still burning when exhaust valve opens flame travels over valve burning and finish in pipes by O2 sensor.bad for valves.burn should be done when valve opens.cam,advance and injection are all tailored for a specific fuel range.unburned air and fuel screw with O2 sensor and cause system to try and correct ,system may not be able to keep it in parameters usually causing other driveability issues.
When I have done this I use math to blend not, 100 %.IE 1gal 93 + 1 gal 110. 93+110=203 divided by 2 gal =101.5.
good luck
