IMO as long as your not doing this to scam someone then who cares. Most people do this either to get a tach (like myself) or to get a different style cluster (SI). Now if you go look at a car for sale and it has say 215,000 and they swapped in a speedo with 60,000 and continued to tell me that the car has originally 60000 I would check the title before you finalize the purchase. If the milage is exemt I would be asking some questions and depending on the price and how it drives I may still make the purchase, even though he lied.
Example. you buy a newer car you think has 35,000 miles but salesman failed to tell you the motor has been changed and has 120,000 You leave the lot 5 years later you sale the car listed with 120,000miles anyways. (motor would be 155,000)
I guess what Im saying is a used car is a used car whether it have 5 miles or 500,000 if it was maintained whats the worry.
My uncle had a brand new f150 work truck he bought motor went before 10,000 lucky he had the warrenty