How to change Exchange email account settings on 50 iPhones, remotely?
Sure, You could use the iPhone Configuration Utility or Apple Configurator to create a profile for the server settings.

Once you've gotten a signed profile document (it can be self signed if you haven't set up trusted SSL certs, etc…) you can email it or post it to dropbox or otherwise put it on a web server for each device to retrieve.

The users would tap the file to download it and then tap to accept the payload. You could leave the account blank so each user would just have to enter an account/password and the profile would have the details on the mail server and settings to be installed.

Start with the deployment page at Apple and scroll down to the Configure section to read more on MDM and Configurator.

http://www.apple.com/iphone/business/it-center/deployment.html

Reading into your settings, you might also consider using directory services or a single sign on solution to pull a person't correct email account from a central directory, but that might cost more than a one time, touch all 50 devices exercise. In the end, you might pay for automation software since it allows better reporting and flexibility as changes like these tend to come more and more often in most businesses.