Q: Can I change my loan officer after getting the pre-approval?
A: Yes you can, even with the same lender, as you can just refuse to do the loan with them unless you are dealing with someone else and obviously they'll value your business over a loan officer's feelings. However believe it or not, that loan officer has done some work, and so I wouldn't be surprised if he would share in the compensation somehow. But really your concern should be that your loan is handled properly, which it hasn't been to your satisfaction, so if you've brought this up and it's been more or less dismissed by the loan officer, it's now time to seek out their supervisor/manager and ask to be assigned a new loan officer as there seems to be some differences in work ethic expectations. The supervisor will likely either then play an integral role in your remaining loan process or assign it to a different loan officer.
Q: He works at a bank, can I file a complaint against him?
A: If he's violated a law of some sort, yes you can file a complaint with whatever agency has jurisdiction over the loan officer/the law that was broken (whether it's a RESPA violation, federal regulation, a state disclosure violation, etc.). You can also voice your displeasure in an email, and what I usually recommend is to write it out on your computer, don't hit send yet, but call up and speak to a manager, use the letter as your guide to state your position in a clear and objective manner, and email it at the same time you are talking so they know you have taken this lack of respect very seriously.
Elaine, here is is a very detailed explanation on the current Good Faith Estimate, including which 6 items actually constitutes a loan application that requires the GFE to be sent out within 3 days: http://www.trulia.com/blog/shanethemortgageman/2011/06/understanding_the_new_2010_good_faith_estimate
Like Scott says, if you were just pre-approved/pre-qualified, then the GFE wouldn't be sent out until the required information for the application is known.