South Carolina keeps you to the coverage on the vehicle involved, pays UIM for damages above the other driver's limits, and bars a consent-to-settle clause
South Carolina's rules are in S.C. Code 38-77-160 (UIM and the vehicle-involved rule), 38-77-150 (basic UM) and 38-77-140 (minimum limits). The deadline is in 15-3-530 and the extension for minors in 15-3-40.
Read how stacked and single-limit coverage differ in South Carolina, check what section 38-77-160 says, or see how South Carolina UM and UIM work.