Originally Posted by
JennyZhu
Okay

it means I am allowed to check in baggage as long as I paid for it, right..Thank you!!

Correct. If you prepay for the luggage you plan on checking in, it will cos approximately the same as the price difference Go/Go Light, thus no need to incur change fees for the ticket.
The baggage fee can be paid online on the SK homepage. The lower rate (NOK 239 appr. GBP 20) must be paid at least 22 hours before departure. If you wait until you check-in online or get to the airport, the fee more than doubles, from NOK 239 to NOK 540 (appr. GBP 50)