I know that the GFE is an estimate of known facts at the time of application. If during the course of the transaction the borrower increases the amount of the loan request by a significant sum (10,000) then is this considered a new application and a new GFE required?

Your application procedures would dictate whether you have taken a new application. If you have, then you must redisclose everything, not just the GFE, pertaining to new application.

If your application procedures treats it as amendment to the existing application redisclosure would not be required; but if there are "significant" changes it would be good customer service to do so.