Modifying pending order approval process

I am looking to collect a bit of data from the user when the sign up. I then want to validate that information from an external DB. I would then like to accept or reject their pending order based upon the DB query truth results.

Has anyone done this before? I am sure that somebody must have. Is there a simpler method I am missing?

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I should say that I am looking for something that will not get over written every time I do a WHMcS update.