I just found out something interesting.
Not anything to do with GS500, but still useful to people, so thought I'd share . Particularly since a web search for this stuff turns up really useless answers, pointing to other forums 

The folks that make HP limiter kits for UK learners permit, http://www.fiinternational.com, can sell to you directly, if you are not in the UK.
They have kits for practically every bike, but, I asked them about a limiter kit specifically for a triumph daytona, and this is what they said:

Quote
Good morning

We can supply to you direct as its outside the UK. We have the 25kw and the 72 kW kits listed for this bike. The cost is £179.99 for the kit and £14.99 postage.
Hope this helps.
Regards
Lisa
F I International.

(72kw would appear to be, for "under 100hp" insurance reasons )

(edit: What the heck.. I thought I modified, but instead I reposted and quoted. Doh.. delete this post!)

If the insurance company accepts this solution I wonder how far you would have to go to prove it? Visual inspection? Dyno-test? Maybe just the reciept for the thing. Or would you have to get it titled as an 'under 100hp' bike.

The way it works in UK (and presumably australia), is that you have to get it installed by "a professional" (and they have to sign a certificate/affidavit/whatever). Then I'm guessing that the insurance company(and the government) makes the assumption that you are NOT a professional mechanic, and so "arent capable" of undoing the mod.

I'd imagine a similar gentleman's agreement would be sufficient, if there are any insurance companies in the US who are willing to work with you on lower rates for HP mod.

It wouldnt make sense to me that you could "retitle" a bike as different. To them, I would think either it's a "Suzuki XYZ", or it's not.

Not quite how it works here in Aus, unfortunately.

The bike models are the same, but they are classed differently, either LAMS or Non-LAMS, depending on what the manufacturer decides to do, and if it matches the power to weight ratio that the RTA decides is the benchmark. And it has to be less that 660cc too.

If you want to de-restrict a bike, you have to cancel the registration of the vehicle, have it safety checked, and re-register it. All in all, about 500 bucks worth of work.

Safety Check: $30 bucks
Green Slip CTP Insurance: $487 for the last one I did on the GS
New Plates: $125
Reuse old Plates: ~$55
Registration: $125

And you could have the bike for 2 weeks, and want it de-restricted, and still go through all that bullshit.

It'll be de-registered as a LAMS bike, which means Learners and Provisional riders can't ride it legally. I'm not too sure on the restricting part. Not sure if the Roads and Traffic mob would even know about it. Not to mention that the restrictions are bullshit on their own. The new 300cc Ninja has more power then its 650cc brother, all because of the physical restrictions on bikes above 500cc. It does fill me with glee when some knob on his L plates pulls up beside me on his 650 Ninja and wants to show his mates how quickly he can blow my GS off. I swear I could hear some of them crying into their helmets when they realize what they have to ride for the next 3 years...

Part of the reason I bought the GS was so I didn't have to go through all this shaZam! when I got onto my full licence. It's already a full powered 500cc, and it's got more then enough poke for what I need.