ok i dont know if this can be done basically i have an astra mk3 wiv no rev counter but i want the dash with it

if i get one from wreckers however i will have to change over at m.o.t time coz it reading a false mileage is there anyway you can replace the mileages from one clock set to other i take it you cant but there are mad people in world who might have

plus has any1 done the non rev counter to rev counter conversion is it easy and is there anythink i need 2 look out for as sum1 told me u need close number from dash unit that w=blah blah blah

help me plz