Stuck my fingers up the tailpipe of my car and probed!

Took my fingers out and they are black and sooty.

Also, the is a rim (1/2 inch thick) of block soot on the exterior of the tailpipe end (wierd).

Is this an indication of running rich?

I read somewhere that to test the O2 sensor, one could disconnect it and see if there is any change to the engine running.

If there is no change with the O2 sensor disconnected, the sensor is fried.

Is this test valid?

Also, is there a convenient way to disconnect the O2 sensor from the engine bay or cabin?