Ignition wires are typically replaced on an as-needed basis. I personally have no rule or schedule for replacing ignition wires. One criterion is if the car runs sluggishly during wet weather. Open the hood at night with the engine running and you may see arcing from the ignition wires.

If the wires/plugs have been on there a long time he may potentially run into problems. One is that the boots may be baked onto the spark plugs. I usually first break that bond before removing the wire end from the spark plug. But since he's going to replace the ignition wires this really isn't a problem. The worst problem he can get into over his head is that the spark plugs may be hard to remove. The threads have a tendency to gall to the aluminum head, resulting in stripped threads on the head. It takes a certain feel from experience to know when the threads will strip.

When he puts everything back together, it is good practise to butter the inside of the spark plug boot with silicone grease so the boot won't bake on the porcelain, and put some antisieze compound on the spark plug threads to prevent galling. This'll help tremendously for the next time this job is done.

__________________
95 E320 Cabriolet, 159K