In SQL Reporting Services when using the web ReportViewer control I had the problem of my reporting not showing when changing ReportServerUrl and ReportPath. It turned out that I hadn't set ReportViewer1.ProcessingMode = Microsoft.Reporting.WebForms.ProcessingMode.Remote.
OK, so that part doesn't have anything to do with changing the properties, but after that I found that after I fixed that problem I could see data for the report, but it would not change the report display when changing these properties. It turned out that I needed to call the Refresh method. I had been looking for something similar to that, but was looking on the ReportViewer control itself. It turns out it is on the ReportView.ServerReport object.