I created small registry editor for windows mobile devices. With it you can browse your registry and perform whatever change you wish. It supports string, binary, DWord (32-bit), QWord (64-bit), multi-string and expandable-string data types. Additionally to that, there is support for both Smartphone (Windows Mobile Classic) and Pocket PC (Windows Mobile Professional) platform in single executable.
You can download first beta here (cab installer) [2009-04-21: final version is out]. In order to run it, you may need .NET Compact Framework 2.0 or higher (if it is not already installed).