It's good to add new custom actions on the nemo wiki page, but I don't really understand the meaning of your archive action.
What is the meaning to rename a file and even a folder by changing its extension by archive?
And why to use a python script to rename a file while to use the mv bash command seems to be easier and more natural?
I use the archive script to tag a file/folder by changing its file ending in order to move all archived files to a backup folder in a second step.
Using the python script was required as explained here: https://github.com/linuxmint/nemo/issues/246#issuecomment-15681032
Furthermore it is a good example to show working with python scripts.