Standard workflow templates are more an example of how the process could be implemented then a process to be done as it is. there are exception to this (SAP SRM and GRC systems for example) but in most cases you simply create your own template and there is no need for program exits.
It is also possible to make some changes to the standard workflow templates using transaction swdd_config. see Workflow Configuration - Embedded Processes (SAP Business Workflow) - SAP Library .