Is it safe to remove earthing from a scope?
The best answer is to isolate the equipment you are trying to measure.  When it is isolated, you are free to ground any one point, which will be done thru the scope probe ground lead.  That keeps the scope, its chassis, and anything it may be connected to or touching from becoming live.

If isolating the circuit you are trying to measure is not possible, then a portable battery-operated scope is the next best option.  These are intended in part for this sort of thing, and are usually well insulated, unlike scopes intended to sit on a bench.

If you are really really careful and can ensure everyone else around you or that might enter the room will be really careful, then you can put the isolation transformer on the scope.  Before you do that, very carefully make sure the scope isn't touching anything conductive, and there are no connections to is to elsewhere, like a USB connection to a PC or something.  This way you get what you suggest without modifying the scope.

I just can't recommend what you suggest.  You may think you found the only connection to ground, but the scope wasn't designed to be modified like that, so you don't really know without testing.  A Hi-pot test would tell you, but may also blow up the scope in the process.

Do it right.  Use a isolation transformer, preferably on the equipment under test, not on the scope.