Managing Active Directory does not always have to be complicated. If you are spending more time trying instead of doing, then it's time to look at something else. For nearly 20 years, AD admins around the world have used one tool for day-to-day AD management: Hyena. Discover why
go into control panel
open Mail
click on Show Profiles
Now click on Add to setup a new profile. Setup the user's email with the new settings. Then you'll go back to the window where the profiles are listed. change the selection from "Always use the following profile" to "Prompt for Profile".
Now open Outlook back up so that it prompts for a profile. select the new one & see what happens. If it takes & everything is where it needs to be then go back into the Mail settings in Control Panel & set it to always use the new profile instead of prompting. Don't delete the old profile. there may be some type of setting from the old profile that you may have to go back to & reference.
Try it on a test user or yourself before doing it with his. that way you'll be able to go in there with confidence.