I'm planning to use my BA miles to book HNL-LHR via LAX for July 20 of next year, of which the first leg will be on AA (BA doesn't fly to HNL). It's a great deal because it only costs the regular 25k miles one-way, which is the same as JFK-LHR would cost, for example, even though a money-purchased ticket would be significantly more expensive from HNL than JFK. The only problem is that I want to do it as far in advance as possible (as soon as the dates open up), since summer rewards inventory go quickly, and here is what I have found:

BA seems to open up bookings 355 days in advance, while AA opens them up 331 days in advance. In other words, July 20 flights become available the preceding July 30 with BA, but not until August 23 with AA. With summer availability as it is on rewards flights, it is very likely the LAX-LHR leg of my journey would be no longer available by August 23, and I wouldn't be able to book the flight.

My proposed solution: on July 30, book 3 or 4 reward tickets on the LAX-LHR flight I want (I have enough miles to do this), and then on August 23 cancel them all and hope that at least 1 comes back into reward inventory so I can book the whole flight with HNL as my origin.

I know rewards inventory can be tricky, and that this is by no means guaranteed to work, but I think it's more likely I'll get the flight this way than if I just wait until August 23 for the AA portion to open up and hope the whole itinerary is still available.

My questions:

1. Has anyone ever done anything like this, or at least canceled a BA rewards flight and seen the reward availability show up again?

2. Does anyone know the cancellation fee for BA, and whether it applies to each ticket or just each booking? I can't seem to find it on ba.com.

3. Does BA actually refund the taxes paid, or do they just credit them for use within a certain time period?

4. This is all based on the premise that you can't change your origin on a rewards flight itinerary change, which I believe I read somewhere about BA. Can someone confirm?

Thanks in advance for your thoughts.