Yes, you can add segments; you can also have AA reissue the ticket if you want to use AA over the Pacific or Atlantic in lieu of JL or BA. Of course you will pay additional taxes/fees for the new segments.

Out of curiosity, how much did you pay in BA fuel surcharges (YQ on the tariff listings)? That's one of the big disincentives to using BA for RTW issuance; sounds like you had little choice in the matter however.

As for IST-MNL, you might consider IST RJ AMM RJ HKG CX MNL. I think there's a several-hour layover at Amman, but it might be quicker overall than trying to get to from IST to Helsinki.

Welcome to the world of BA RTW "desks." Oy.