changing your mind about recommenders

[wootfan]

I posted this to the econ admissions part of the forum, but only got one response. But it's not specific to econ, so I thought I'd post my question here too:

After I list a professor's name on the online application, can i delete him/her and replace him/her with a different recommender before I actually submit my application?

Thanks!

[wootfan]

oh, this is kind of urgent so if you can help, then i'll be very grateful.

i need to know because one of my recommenders (let's call him prof A) has disappeared off the face of the earth. Back in May prof A promised me a strong recommendation letter, but now he's not answering my emails, and it's getting closer and closer to the first deadline. So I've been thinking that I should replace him with a different prof. (prof B). Prof B will write a good letter, but I'd prefer Prof. A. because he knows me better. But I'm wondering if I submit Prof B's name right now (because I need to give him sufficient time to fill out all the forms), can I replace him with Prof A if Prof A happens to reply within the next few days?