My recommendation is to create an entirely separate instance of OpenERP that you can use as a development environment, ideally on a different machine. Download the source code from nightly.openerp.com: openerp-7.0-latest.tar.gz. This is makes writing code way easier, since the permissions will all be set to your login account. Then you can start and stop easily on your own.

The alternative would be to stop the service, then find the location of the openerp-server file and run it manually:

openerp-server -c my_config.conf -d my_tb -u my_module

Either way I'd recommend downloading the source code directly, it's less hassle in the long run to work with IMO. Here's a nice guide on that: http://www.theopensourcerer.com/2012/12/how-to-install-openerp-7-0-on-ubuntu-12-04-lts/