How to programmatically modify assemblyBinding in app.config?

I found what I needed. The XmlNamespaceManager is required as the assemblyBinding node contains the xmlns attribute. I modified the code to use this and it works:

    private void SetRuntimeBinding(string path, string value)    {        XmlDocument doc = new XmlDocument();        try        {            doc.Load(Path.Combine(path, "MyApp.exe.config"));        }        catch (FileNotFoundException)        {            return;        }        XmlNamespaceManager manager = new XmlNamespaceManager(doc.NameTable);        manager.AddNamespace("bindings", "urn:schemas-microsoft-com:asm.v1");        XmlNode root = doc.DocumentElement;        XmlNode node = root.SelectSingleNode("//bindings:bindingRedirect", manager);        if (node == null)        {            throw (new Exception("Invalid Configuration File"));        }        node = node.SelectSingleNode("@newVersion");        if (node == null)        {            throw (new Exception("Invalid Configuration File"));        }        node.Value = value;        doc.Save(Path.Combine(path, "MyApp.exe.config"));    }

Sounds like you've got your configuration file tweak working now, but I thought you might still be interested in how to adjust binding redirects at run time. The key is to use the AppDomain.AssemblyResolve event, and the details are in this answer. I prefer it over using the configuration file, because my version number comparison can be a bit more sophisticated and I don't have to tweak the configuration file during every build.

I think the right Xpath syntax is:

/configuration/runtime/assemblyBinding/dependentAssembly/bindingRedirect@newVersion

(you have a slash too many).

Or if this doesn't work you could select the bindingRedirect element (using SelectSingleNode):

/configuration/runtime/assemblyBinding/dependentAssembly/bindingRedirect

Then modify the attribute newVersion of this element.