<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by pegasus8228:
to change the first flight, u have to reissue the ticket.
(mainly because the tkt validity - 1 year -- changes accordingly)
to reissue, it is free of charge.
it just takes up about an hour at the ticket office. this is equivalent to a refund and a new ticket (plus the fare does not change)and there is no charge.</font>
You are absolutely correct for tickets originating in area 2 and 3; the rule is different for area 1 (surprise, surprise). For area 1 (Americas) no changes of any kind are allowed to the first international segment (or prior segments, if any). The original question was for a ticket originating in GIB, which is area 2, hence changes in date and routing are allowed without charge prior to departure. BA's claim that the issuing TA must make the change is plausible (but I'm not an expert to make that determination).