I'm heavily into Microsoft BI suite. Seems the Deploy function of SSRS works great, in that you can specify OverwriteDataSources = False in the Project Properties.
Aside: (Yeah, you still get a WARNING that says:
Deploying data source '/Data Sources/<MyDataSource>'.
Warning : Cannot deploy data source <MyDataSource> to the server because it already exists and OverwriteDataSources is not specified.
even though you TOLD it NOT to Deploy said DataSource. But this issue is listed under another Feedback.)
Moving on, When you Deploy in SSAS, your DataSources on the server get overwritten. There is NO ability to switch between dev/test/production scenarios.
The only option you have is to BUILD the project to a folder, then MANUALLY edit the <projectName>.ConfigSettings files (and possible others), then invoke the SSAS Deployment utility.
Too many manual steps, especially if you have multiple DataSources and multiple ReportActions.