To answer one of your questions, yes you may set a code if you do not ground the plugs. I have a different solution than most for when I need to turn over the engine for diagnostic reasons. You can make a remote start switch on the cheap here which does not require the ignition to be turned on. Using any kind of on/off switch and two long wires. To the end of one wire add a female spade terminal to match the terminal where the green wire is located on top of the starter. On the other wire add a small jumper cable type clamp. This will be attached to the main battery cable on top of the starter. Now simply flip the switch to turn over the engine as needed. I do remove the plugs also.
Neat idea that, thanks for sharing.
