This is definitely an old post now, but it still might be useful to have an answer.
I had kind of the same issue, I wanted to add the existing field "Work" to the "Entry" Table. I managed to add it, but it was not showing in the table.
Now, to apply the changes, I simply open the table again by calling the TableApply method:
appProj.TableEditEx "Entry", True, , , , , "Work"
appProj.TableApply "Entry"
It works fine for me.