I've changed dates on first flight of RTW several times without problems. I bought ex-KEF RTW's late last year that I keep pushing forward. As long as there are no re-routes you should be fine.

Remember - it's only the first segment that are "locked". Fly ICN-SFO and then re-route without problems, you only pay the changes in taxes plus $125 USD changing fee.

Tickets are refundable as you mention with $125 USD penalty.