I am a novice at OneWorld RTW tickets, and probably shouldn't even try my hand at answering. But I am curious, so I went to FewMiles website, where he lists the rules for ticketing. Copying from that:
18N CHANGES/ 1.PRIOR TO DEPARTURE
19N . TRAVEL ORIGINATING AREA 1 -
20N . - BEFORE TKT DEADLINE - PERMITTED WITHOUT
21N . PENALTY. CHANGES TO THE 1ST INTL FLT OR
22N . PRECEDING FLTS REQUIRE TKT REISSUE.
23N . - AFTER TKT DEADLINE - CHANGES TO THE
24N . 1ST INTL FLT AND PRECEDING FLTS ARE NOT
25N . PERMITTED. DATE/TIME CHANGES TO OTHER
26N . FLTS PERMITTED AT NO CHARGE. TKT MUST
27N . BE REISSUED.
Since you are past the ticket deadline - at least for the fare at which you ticketed - is it possible that the first international flight is considered to be the one OUT OF EUROPE and thus the flights before leaving Europe cannot be changed?