I have a few old applications I made that are all under the same dev ID. I'd like to separate them out to be on different IDs. Can I just rekey my device, package the application again, and replace it? Will Roku prevent me from replacing the app unless the dev ID matches with what was already there? I'm aware that any registry values would be lost.
You can do that, sure. I would recommend increasing the version revision file in the manifest so you ensure all your users get the new app -- not sure if simply changing the packaging key will be seen as an updated file otherwise.