If you do what you suggest - one at the 80K level then go back and do a second at a higher level, hopefully the second will be at 125K miles. But as was said, you can always cancel within 24 hours.
I am going to guess that once you book the 1st ticket at 80k, wait some time or use another computer to book the 2nd ticket.
You may be able to get the 2nd ticket at 80k too!
Failing which like we have said " You have 24 hours to cancel".