I wouldn't trust that the card issuer's insurance packages will apply. You can't really *change* a ticket into a RTW -- you'd most likely end up canceling the original ticket and get a voucher. Then you pay for the RTW with a combinatinon of voucher (not even a discount coupon, but a cash coupon) and credit card, but most CC insurances insist that you pay the price with the card in full.
Which you have done via my [patent pending] process.
When you cancel (not refund) a ticket, the PNR (Passenger Name Record, a.k.a. reservation: the 6 digit alphanumeric thingamajig) still exists and can be changed. There is no "new" reservation; you simply pay a for the change in fare. The PNR is still the same as the original (though the eTicket number may change). Whether a normal one-way or round trip can be changed to a RTW ticket is a question that I cannot answer. I can say that it can be changed to different routings, rules, dates, etc., etc. without the use of vouchers.