Thanks so much for the python help!
I was able to get the code working using the array rather than the left, mid functions.
Here's the code I used:
And of course I was using the wrong parser for the !<your fieldname>![0:2] + !<your fieldname>![-1:] expression. It works fine and I'm sure will come in handy.
txtList = list(txtstr)
if (txtList == '0'):
txtList2 = txtList, txtList, txtList
txtstr = ''.join(txtList2)