If you want to contribute to this plugin you might want to build any changes you made on your local machine and try them out in your JOSM installation. Please follow this description on how to set up a local developing environment for plugins.
As this plugin is maintained in GitHub and not in the JOSM's branch of OpenStreetMap's SVN you will also need to fork this repository and then clone it locally into a folder that's within the plugin directory of the JOSM branch.
Even if you have write access to the JOSM SVN please do not commit this repository there - because I don't and thus can't make any corrections there! Thank you!
Questions still unanswered? Please do not hesitate to contact me via [email protected]!