Make sure you define your replacement strings in order from most characters to least to avoid changing Pt.III to 1x01II eg:
Code:
Pt.III -> 1x03
Pt.IV -> 1x04
Pt.IX -> 1x09
Pt.II -> 1x02
Pt.I -> 1x01
Pt.VIII -> 1x08
Pt.VII -> 1x07
Pt.VI -> 1x06
Pt.V -> 1x05