I am going to have to extend my vacation in Ireland for a week to include a week of work. I bought my original tickets weeks ago (~$880) and now that I heard I will need to stay an extra week, I need to change my return flight.

I called Delta and asked about changing my return date and it will cost approx. $950 + $250 change fee; whereas, a one way from DUB to LAX is approx $600.

Should I be more worried that Delta may see a second flight booked from the same location a week later and be more likely to either charge me a fee or change/affect my second booked flight home?

I can get a similar flight using American for similar price, however, I would prefer to fly DL and get the miles from a return flight. Is flying American a better option or most likely make no difference?