You can change the number in most *A lounges even if the lounge does not have the facility to reprint - but YMMV - I had one lounge change one sector but not the next on a 2-sector flight, while another wrote the numbers down but clearly forgot to do it before take off as my A3 account received the miles. So better to change on check-in, that way you can be sure where the miles will credit as you see it printed on BP.
In some airports you can also get a BP printed/change FF nos at a transfer desk - useful for those multi-sector flights where the mileage credit from different sectors needs to be split.
Most *G carries seem OK to give *G benefits on sighting the card on check0in even if you are crediting another carrier - I've found LH, A3, SQ, NZ all OK with this personally, though there are reports that some US carriers don't like this.. If only they were all like NZ and LH and could accommodat different entries in FQTS and FQTV which is a tidier way to do it.