The following two different methods should work for reading the values:
text1a = jso.xfa.form.form1.subform.FirstName.rawValue()
text1b =
jso.xfa.ResolveNode("form.form1.subform.FirstName").formattedValue()
And, the following line should work to modify the field value:
jso.xfa.form.form1.subform.LastName.rawValue = "NEW VALUE"
These lines are copies (I just changed the two variable names for the first
two lines) from an Excel VBA project I worked on last year. I just checked
with the current version of Acrobat XI (and Excel 2010) and the code is
working and will extract and set information in an XFA form.
You will need to understand how data is stored in an XFA file in order to
access data in the XFA format.