SQL Server : Changing Database Username
Windows logins are tied to Windows users/groups based on the SID. In other words, you're still able to log in since the Windows user's SID matches, even though the login name still indicates the system name rather than the domain name. If you're worried about the mismatch, you can drop and recreate the login. Since it'll have the same SID, it should map to all the existing database users, and privileges will be preserved. Also, Management Studio seems to think you can hit F2 to rename a login, but I don't have a test system handy to confirm that works.

Of course, all the database users will still have the old name too. You can either script/recreate them, or try the F2 method.

After you've done all this, you'll probably need to change the owner on the jobs. I usually keep all the jobs owned by SQL Server logins (typically sa) so that they don't all fail if there's a temporary problem with the DC.