duplicating weight method

i need to duplicate the weight method for each of these,

• singapore post registered parcel (weight + registration cost)
  singapore post unregistered parcel (weight only)
  japan post registered parcel
  japan post unregistered parcel

i duplicated the files, and replaced all the 'weight' terms, but it ended with errors. i managed to duplicate other methods, so you can say that i basically know what i am doing.

i suspect some of the 'weight' terms refer to weight itself and not the weight method name. so the former should not be replaced. looking thru the files, i cant be sure which exactly refers to the weight itself.