There are no rules as such, but Waze does seem to like seeing the community contributions (well, most of them).
The very first addon script was demonstrated by Waze themselves at the Paris meet one year ago.
There are a few plugin developers now, but no designated place for discussion or collection of resources yet. It's been suggested, though there's possibly a feeling that it should maybe be kept a closed community.
Out of interest, what does your script do?Edit:
I found your script, which looks like an aid for looking up addresses and entering them into the editor. We have a similar script for the UK.