For the integration between SCM and Work Items consider looking into https://jazz.net/products/rational-team-concert/ and https://jazz.net/products/rational-team-concert/#features the integration between them is really simple to use.

To configure available preconditions look at the Process Configuration>Team Configuration>Operational Behavior especially the Source Control section.

For how to create own behavior have a look at https://jazz.net/library/article/1000 although this is for work items, it follows the same concept. There are examples for custom preconditions and follow up actions for SCM in the SDK section of the Wiki https://jazz.net/wiki/bin/view/Main/RtcSdk30 . https://rsjazz.wordpress.com/2012/07/31/rtc-update-parent-duration-estimation-and-effort-participant/ provides some links to other resources, for example the operation ID's.