Depends on why you are converting.

If you just want to get use a starter box then you do not have to do anything to the engine. Just leave the pull start on there.

If you are looking to get more power out of the engine by removing the pullstart parts, you are going down the wrong road.

The power increase is not significant at all, you may not even notice it unless you were to also install a lightweight flywheel.
Then you would notice some increas in RPM.

To answer the question directly, yes you have it right.
It depends on the type of engine though, some engines have a seperate shaft that protrudes for the pull start. In this case you just remove the rear shaft and install the non pullstart backplate.
Others will need to be cut, NOT filed, you will need a dremel tool with a cut off wheel.

Like I said you might as well just by a non pullstart engine, removing it is just not worth the trouble.

Dbow