I called 3888 but I guess since I asked such a hypothetical question they couldn't give a concrete answer, just said 1 month would be much easier than let's say 6.

Let's say if I have enough AM to issue the first itin but not the second yet, can I reissue to the higher band later? I assume it will be a $100 reissuance fee and must be done before the first flight is flown. Keeping the same original routing as well.

So, from
CDG-oHKG-oLHR-oZRH-oHKG-LHR//BCN-CDG
to
CDG-oHKG-oLHR-oZRH-oHKG-LHR//BCN-CDG//HKG-oHND-xHKG-xLHR-CDG