Some installers insist on both... I personally do exactly as you described, just the tracking fix.
You'll read of people claiming to have had their focus coil fry. In about 60 installs, hasn't happened to me yet.
The focus fix does not cause damage. It reduces voltage on the circuit... that's all. No damage is caused by this.
If the console works after a fix is applied, you've successfully applied it. There is no better test than that.
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Oshawa modder... up there in Canada.