For scripted updates it would be useful to have the ability to set variable values intelligently within a recipe. We already have code to do this in meta/lib/oe/recipeutils.py, we just need to add a subcommand in recipetool to provide access to it. There should be an option to select whether updates to included files are allowed or not.
Now implemented in master (also relies on a bunch of the other commits merged around the same time): http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=b381f804a541bb1d08e331c139a82e250f924c05