Yes it is possible to do that.
if its regular gas
to put the oil in the lawnmower's crankcase would be fine, so long as it is an appropriate viscosity.
You get engine damage from lack of lubrication
put a bomb in it or you can pour gas all over it and set it on fire
0.6 litres
Drain the oil and gas out of the crankcase and put oil back it should be OK
It depends on what is wrong with the gas. It probably won't.
15x8 tire = 14.4 oz.
Apparently you didn't crank it up. You are still here. Nothing except it may clean out some old dirty oil. Remove the gas and the oil and discard same. Refill the oil section and refill the gas tank. Don't do that again.
The engine floods and you have to wait for the lawnmower to drain before you start it up again or it might start smoking.
If the lawnmower has two compartments one for gas and the other for the oil, then put gas in the gas and a 30w type oil in the oil compartment. Simple as that. If you have an engine with only one compartment then you'll need to check on the manufacturers suggestions which is usually 40:1 or something close.
No. Fuel tank needs to be dropped and entire fuel system flushed.