The cost center assignment is made in the TIME DEPENDENT tab of the asset master data and can be set for specific validity period. The validity period is important because an asset can belong to one cost center for specific time period and then belong another cost center in different time period. And SAP System allowed you to set up asset as not time dependent if the assets will always belong to the same cost center.
To disable the time-dependency of cost center in the asset master record you can go to the SPRO Trasanction code.
Financial Accounting(NEW)-> Asset Accounting->Master Data->Specify Time Dependent Management of Organizational Units
The new screen will show, and if you checked TIME-INDEPENDENT Organizational Units, the system disable time dependent functionality.
if Time-Independent Management of Organizational units is unchecked this means when you enter cost center assignment for an asset it is valid for all time intervals. If you change the cost center with this setting active, the SAP System will create an automatic transfer document from old to the new cost center.