Using user-selected class in an ability

[Predictably Damaged]

I am trying to implement an ability which lets members of races with the ability cast spells as if they were higher level in a class of their choice. I have a drop-down selector for the class, but am not sure how to use it. As I understand, my script should look something like this:
hero.childfound[cHelpWiz].field[cCasterLev].value += 4

Except that I need to replace "cHelpWiz" with "field[usrChosen1].chosen", as follows:
hero.childfound[field[usrChosen1].chosen].field[cCasterLev].value += abValue

which throws the error "non-existent thing 'field' used by script."
Could anyone explain how to do this?

[dwobbit]

Something similar to this should work:

doneif (field[usrChosen1].ischosen = 0)
hero.childfound[field[usrChosen1].chosen.idstring].field[cCasterLev].value += abValue