Task runtime data can also be migrated. Advantage has an article on it
Using the Tasks migration portlet (Administration->Admin Dashboard->Migration) will move task instances from one MWS to another once they are running. (After you deploy the task applications)
As stated above you need a new instance of MWS pointing to a fresh DB.
This means a new
• Database user name AND
• Database name or tablespace name
If you change the tbl space name remember to do update all scripts.
Tip: mws new -Dserver.name=INSTANCENAME … if you don’t type instance name it will use Default (Which is the one already in use unless you changed it originally).
Upgrade documentation is good and worked for us when we did 7.1 → 7.1.2
I just had do this myself due to a corrupt user which is referenced in a table “somewhere” where “somewhere” is undocumented. So I did a migration one instance to another same version 
#MWS-CAF-Task-Engine#webMethods-BPMS#webMethods