I've never, ever seen a homeowners policy to exclude ONLY the shingles on the roof. That just tells me something else is going on, that you didn't mention - and maybe that you don't know.
If you refuse to sign the exclusion, the insurance company is going to cancel your policy. There's NO WAY that the roof is covered, because nothing HAPPENED to it. That's the whole point - the insurance thinks you need a new roof, and thinks you're going to put in a claim for it and want them to pay. Insurance does NOT pay for maintenance items, and they think the roof needs to be maintained.
So, if it were me (and you didn't ask, I know) what I would do, is call the agent. Explain you have a report from a licensed roofer stating the roof is in good shape, can he send that in, and get the insurance company to accept that, without the roof exclusion. You flat out do NOT want a "roof exclusion" on your policy - and I haven't even READ it, but I'll tell you, you don't want it anyway.
If the agent has no luck, do NOT tell them you're not going to sign it. What you need to do, is IMMEDIATELY start shopping out for new house insurance. Call some more agents, be honest, explain the situation - you have a licensed roofer that says the roof is ok, but your insurance company wants it replaced anyway (hmm. How old is that roof? Average roof life for a shingle roof on a 8% incline or greater, is going to be about 15 - 20 years). Get your new coverage BEFORE the cancellation notice is issued on the old policy. Leave lots of time to shop, because you might need it.
When the old company cancels your policy, they WILL return your premium.