I did it at the ECU (about 4" past the connector) and had no issue.
by interrupting the signal, your not doing anything different then the signal to shut it off when the key goes to off. If you try it and it has an issue, undo it and it should reset. Try it first by "having a loose wire" (run the car and pull the wire out of the plug... if it shuts down put in back in and try to start. if it does then you got the right one.
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