I'm not sure in which languages those extensions are, I think the are written in Html, Javascript or JSON. As far as I know they are "compressed" in a .CRX file.
It is possible to directly modify the html, js, json of a Chrome Extension (or whatever language they use)?
I searched it in google and i found this
The Google Chrome Extension file type is CRX. It is essentially a compression format.
So if you want to see what is behind an extension, the scripts and the code, just change the file-type from “CRX” to “ZIP” . Unzip the file and you will get all the info you need. This way you can see the guts, learn how to write an extension yourself, or modify it for your own needs. The you can pack it back up with Chrome’s internal tools which automatically create the file back into CRX. Installing it just requires a click.
Note that some zip programs have trouble unzipping a CRX like sathish described - if this is the case, try using 7-Zip - http://www.7-zip.org/