you can create this jython script and assign to the import format:
return ("0" + strField.split("-"))[-2:]
this function splits your strField using "-" as delimiter, then concatenate "0" with the second element ( as array starts in position 0), and finally take the last two chars [-2:]
If you have 1 digit after the hyphen you will get 0x. On the other hand if you already have 2 digits, you will get xx
Hope that clarifies.