EDIT: I wrote this post because of what I found while trying to find a way to solve Sarek's dialog problem in the beginning of the game. Seems like I didn't read the other posts correctly and this was already common knowledge. Well, at least it can serve as a reference?

Basically, as others have shown, the RVM and RVR are ZIP files. However, it is created with NO COMPRESSION.

You can UNZIP it into a temporary folder and edit all files to your heart's content. Just remember to turn off READ-ONLY for each file, before you edit, and then turn it back on afterwards (in the case of the RVM I noticed the files were read-only).

--->>> Just don't forget to MAKE A COPY of whatever RVM you are about to edit so you can restore it if something goes wrong ;) <<<---

Then all you have to do is repack all files back into a ZIP file, again with NO COMPRESSION, and rename it to the original file's name, extension included, to substitute the old RVM.

Have fun "modding" the game :P