It is unfortunate that the output wire insulation gets so brittle with age. But, that is just one part of the whole assembly, and doesn't mean the whole assembly needs replacing because one part if it is damaged, anymore than a whole car needs to be replaced because the tires are worn out.
It is NOT a simple task to change the output wires. But, if you can the coil will still work fine for many more years.
The coil is made of copper windings, copper doesn't degrade with time, only exposure to the atmosphere. The copper windings are coated with and insulation layer. could be Formvar, shellac, lacquer, epoxy, etc. The insulation may also degrade with exposure to the atmosphere or UV light. But, until it breaks down the copper is protected. Then the entire insulated wire coil is sheathed in yet another molded plastic, to protect the individual wire insulation from the atmosphere and UV light. So, as long as that other shell is intact, the innards ought to live and function as new for a very long time indeed.
If the ignition wire join at the coil body is intact and not cracked, you can use NGK's wire splicers to butt new wire onto the oid coils without any dissection. For example:
http://www.parkeryamaha.com/ngksparkplugwiresplice.aspxhttp://www.ngksparkplugs.com/products/performance/splicers.aspSimply drilling into the coil body and stuffing a wire into it, is pure folly and only if you are lucky will it function at all. You need to make a wire to wire connection in order to NOT add another spark gap to the spark loop.
Hope this helps,
