Please do not make any changes to the existing jobs/procedures.
If you wish to perform datamart type operations on your custom objects data, then currently you would be best off by creating your own jobs and procedures separately, mark the jobs you create as 'incompatible' to the regular datamart (this just prevents them from running at the same time if they are scheduled close together, and makes one of the jobs wait until the other completes), and schedule them to run after you normally expect the datamart jobs to finish.
Modifying the out-of-the-box procedures and/or jobs can not only impact your ability to get support for problems arising with the datamart due to the use of unsupported customizations, but also during any patch or upgrade you risk running into clashes and incompatibilities that will be more difficult to back out / reapply or fix. So separation of the customization from the out-of-the-box procedures is strongly advised.