Hi i was wondering how muhc a reissue as follows would cost and could I do it

Currently I have a Done4 and I wish to change some of the segments due to Lan changing to premium economy etc on some of the flights

what I want to do is change to the following

syd-scl-ipc-scl-lim-eze-lhr-ist-lhr-dxb-lhr-nrt-cgk

from

syd-eze-gru-lim-scl-gig-lhr-ist-lhr-dxb-lhr-hkg-dps

firstly is it possible i think it is but I could be wrong

and secondly would it cost anything apart from the $125 USD change fee

and if it did would they reissue the ticket and would I get a refund on fuel surcharge as when I booked it fuel costs were a lot higher

any help greatly appreciated