In any case you want to change the ArcGIS Server account, you do not have to rerun the ArcGIS Server installation. Instead, use the Configure ArcGIS Server Account utility that is included and can be found in the Windows Start menu under ArcGIS > ArcGIS Server > Configure ArcGIS Server Account.

 

 

 

It is recommended to export the setup configuration file and reuse it on subsequent installations of ArcGIS Server to ensure that the ArcGIS Server account is configured exactly the same on all the GIS servers in your site.