Legally, you have 45 days to change your vehicle registration when you move to SC. If you are still using your other address as your official residence the state may never know, but be careful. Most counties have auditors/inspectors that run spot checks and reference other data to catch those who have not paid the property tax.
From the DMV website:
Moving to South Carolina
If you move to South Carolina from another state, you have 45 days to transfer your vehicle title and registration. You may apply for the title and registration by mail. The Form 400, Application for Certificate of Title/Registration, which must be completed, contains the proper mailing address for the department.
You must have the following to transfer your out-of-state vehicle title and registration:
-Your out-of-state vehicle title and registration
-If there is a lien on your vehicle, you must bring the name and address of the company that holds the lien.
-Liability Insurance information
-You must provide the name of your automobile liability insurance company, not the name of the agent.
-Completed Form 400, Application for Certificate of Title/Registration
To complete the form, you must have your vehicle odometer mileage reading and any current lien information.
-Paid Vehicle Property Tax Receipt
-Before you can register your vehicle in South Carolina, you must first pay the vehicle property taxes that are required in the county in which you reside.
§ Title and Registration Fees
Title - $15.00 fee
Passenger cars - $24.00 fee
RV's - $24.00 fee
Persons 64 years of age $22.00 fee
65 or older or disabled $20.00 fee
(If disabled, a statement from a medical doctor as to the permanency of the disability must be submitted)
Motorcycles - $10.00 fee
Utility or Camper Trailers - $10.00 fee
Trailers with empty weight in excess of 2500 lbs. - $20.00 fee
Trucks, Truck-Trailers and Road Tractors (All Property Carrying Vehicles)*
GROSS VEHICLE WEIGHT FEE
(Over 9000 GVW upon request)
* Trucks over 26,000 GVW and buses 16 passengers or more for hire must show SSN or FEIN, but tax receipt is not required.