Remove spark plugs and put diesel in tank?

NO the compression ratio on a petrol engine is lower than a diesel.

No need to remove the spark plugs.  The car will die soon enough.  Diesel needs more than a spark to ignite it.  So you got nothing.  Try it in your lawnmower as they are cheaper to fix.  If you are adding diesel to gasoline that is in the tank, it will mix and you will notice the increased SMOKEPOWER of the exhaust as your car sputters along.   Yeah, pssing in the tank is not as damaging as diesel(pss does not mix with petrol-as it is basically water.)

No. Not a good idea.

With the spark plugs removed, there will be zero compression.  No reciprocating internal combustion engine runs ( even if you're using the correct fuel ) without first compressing the fuel/air mixture.

Yes - car makers add all the extra parts to drive the cost up and make repairs more complicated.

The starter motor will turn it over until the battery dies. The diesel will spurt out of the spark plug holes and make a mess of your engine bay and whatever is underneath.

You will then have an expensive garage bill to get the engine running again on petrol.

Yes it will still run and function normally 

Simple answer is no.  Car will crank and that will be it.

No, and you'll ruin the upholstery.

No.

A diesel engine needs to have higher compression than any gasoline engine.