you could perform a obj-open-by handle method once you have identified the pxInskey of the template rule.
Please note that wrt to template functionality, there are 2 set of data involved, one is the actual Template rule (of type RULE-OBJ-TEMPLATE).
Second is the Template Run data instance (of type PEGAMKT-DATA-OUTBOUND-TEMPLATERUN-FILE).
This is because the pzinskey of the template rule changes everytime a user make modification to the template rule. this will/should invalidate the current template staging data which is pending processing, as it was generated using the prior version of template rule.
The template run data instance will always have reference to the latest template rule under "TemplateInsKey" property.