It is possible. You just need to setup a new project, create a package not named "data", put everything you want to have in the other game in there and compile that new project. The Startup project is quite empty, so compiling does not take much of time.
A real-live example: As we all know, strings for localisable games are normally kept in "string.tab". So, to localise the game without bothering the publishers too much, you just need to get a copy of their string.tab, translate it, setup a new project, create a folder, put your new string.tab in it (yes, it does not have to be connected to your new project ;-) ), promote that folder to a package, set the priority of this package to somewhat higher than original (say, 10, for example) and compile. then ignore all created stuff except your new priority package, copy it to the original game, and voila, your game is localised.
(Well, if the publisher thought about a way to deal with special characters, that is ... but that's not the question here.)
All you need to patch the game is the original filenames of the files to patch, and their content, dimensions for images etc.