Replacing Work Centers in Task Lists 
You can replace work centers
Replacing work centers manually in operations
When you replace a work center in an operation with another, the following data is transferred to the new work center:
The units of measure for the default values are not transferred. The
rules of maintenance for the new work center are valid for the default values.Mass replacement
This can be conducted either online or in batch mode. You can work from the area menus for either Work centers or Routings.

Replacing work centers in routings is described in detail in the R/3 Library PP Routings - Changing and deleting routings as well as Mass changes and where-used lists.