Specify an existing Windows account to be used by SharePoint Server Central Administration tasks to access and modify settings ...

Specify an existing Windows account to be used by SharePoint Server Central Administration tasks to access and modify settings in the configuration database. The following user rights are granted automatically to this account: Replace a process level token, Adjust memory quotas for a process, and Log on as a service. 

Note: Specifying a new account does not revoke security rights from the existing account. For more information, see the Microsoft SharePoint Server 2010 Administrator's Guide.

Important: Changing the configuration database administration account requires you to retype the password for the default content access account and for all rules that include or exclude content. Otherwise crawls will fail.