Using Coupons out of sequence on OWE
 

I have LHR-IST-LHR and LHR-DXB-LHR booked as part of my OWE. Currently the sequence of coupons is as above. If I was to change the date of the LHR-DXB-LHR to a date before the LHR-IST-LHR will I have a problem?

Yes, ticket must be re-issued. But BA has been known to be flexible about this.

Yes - trying to do this without getting the ticket reissued is very risky. But as number_6 says, you might well be able to persuade a BA ticketing desk to reroute/reissue it without a change fee since there is very little work in this (no change to fare basis etc.). BA T4 at Heathrow might be worth a try if you are passing that way - I hav ehad good experience there, and reports suggest that T1 ticketing is less clued-up on ONE tickets.

I did a smiliar thing and got BA to sticker the segments - I think they were happy to do it as they originally thought that they had to re-issue the remaining 35 sectors!