Not clear on Settling to CO. Are you settling to Cost Centers?
Basically by moving WBS you will be trying to rewrite history which is exceedingly difficult and very easy to mess up. You will have to account for all of the different business scenarios and how they post to PS objects and then reverse them and replicate.
Finding a way to split the Networks between the SN and DN side would be much easier. Are you scheduling within these networks? What is the requirement driving having one Network on both sides of the Project?
Since you are just collecting costs and not trying to measure profitability on the project it is easier to use multiple projects and develop a reporting solution.