According to RWS Support it is not possible to reassign the translation and DTP tasks to another vendor during project planning task for a second, third or later batch as it is possible for the first batch of files of a project. From our perspective as a client who can't give the customer the possibility to choose between different project templates during project creation, this is quite impractical, as we often have to reassign translation and DTP task to another vendor during project planning task. This means, right now we either have to create a new project ourselves or have our customers create a new project. 

Please give the possibility to reassign any batch of a project to another vendor during project planning task just as it is possible for the first batch of a project.