The most common approach to make changes to BPEL model is invoke(Callable ...) method. 
Now it always commit changes are done in the nested Callable.call() method. You can see it in sources. But it seems more
reasonable to rollback changes in case of any Exception. The current approach can lead BPEL model to inconsistent state
when only part of changes are applied. 

Moreover, it seems the BPEL model doesn't have methods to rollback changes even manually. Code observation shows that
the method rollbackTransaction works only with XAM transactions. 

It's also good idea to write some JUnit tests for BPEL Transactions.