I have an upcoming BKK-NRT-IAD trip. First leg obviously ANA but a UA codeshare if it matters. Is it known what impact that has on the ability to select open seats from the first two rows?

ill plan to do all of the below, bust wanted to know if anyone knew:

1) check in through ana, then goto united immediately after and change seat
2) same as above but go to ua exactly 24 hours before hand
3) same as 1 but call us immediately after checkin with ana and ask
4) same as 1 but call ua t-24 of nrt-iad leg
5) nothing until the ana flight coupon shows as used

EDIT: No luck so far. ANA can't do anything. UA seat selection is locked out. Called twice, was told not available; EF shows 1A and 1K blocked. I'll just keep checking.