I found the solution...Just to be useful for others who research on this topic - currently it is not possible to customise mail template for task reminder or assignment..
We just have to go with task-reminder or task-assign template in jbpm.mail.templates.xml
This has been raised as a feature request in JBPM forum and is not expected until release of JBPM4..so not anytime now!!
Or customize the jbpm code....
worth a try..definitely..but there are some templates which are resolved in compile time and runtime..
if you really know what ur doing..please do give it a go..there is a JIRA raised for this and they have discussed few options for changing jbpm code..(a bit tricky though)
I already did it once but lost the code due to a crash (did not commit it yet). Changing the code is not tricky at all. It mainly comes down to using e.g. (part of) the task name in the template name with e.g. -reminder as a suffix. Not difficult at all.
Template resolving compiletime? Hmm... Are you sure? Where in the code is this?