If there was not an increase in premium for the increase in value/replacement cost - you be I'd be concerned. I'd also be contacting someone farther up the food chain then a local agent.
Most Honda based trike conversions are covered as accessories just like chrome and other add on items. There is a charge for that... I would hate for you to find out the hard way that your agent thought they knew how it worked.
If the insurance company continues to make that claim then I'd get it in writing along with a signature not just word of mouth.