pre-assigned       
adjective (also preassigned) uk/ˌpriː.əˈsaɪnd/ us/ˌpriː.əˈsaɪnd/
 预先指定的;预先分派的;预先分配的
given a value, characteristic, or purpose before a particular time or activity
  Each member of the team has a pre-assigned role.
 Airline passengers now have to pay extra to get a preassigned seat. 航空公司乘客现在必须支付额外费用才能获得预先指定的座位。 
 All buttons are pre-assigned to the software functions.
 - More examples
 - It was unclear whether the bomber dropped its payload on its pre-assigned target.
 - Each session had pre-assigned discussion topics, making it very unlikely that a debate would develop.
 - Each client workstation copies the backup data to a preassigned location.