Typhoo, why not insure the bike with standard pipes.
Then phone the insurance company and tell them the original pipes needed repalcing and you've just put genuine replacement Triumph pipes on. If they don't ask, there's no need to say they're TORS! But at least it will be recorded on file that you informed them.
I had a very heavily modified Buell, a while back, and each year I'd tell the insurance about a few more of the modifications, but I'd always justify the changed bit.
The seat was changed to give more comfort so I could concentrate on riding.
The lights were changed so I could see better at night.
The pipes were changed to give smoother running throughout the rev range.
The gearing / cogs were changed so it had better pickup at low speeds..
The swingarm changed to stiffen up the back end and give me more control.
Etc etc.
As long as you can justify the change on the grounds of safety (however tenuous that reason may be!) the insurance companies have no problem