Starting June 20, it will no longer be possible to change your manufacturer's affiliation contract during the test season and pre-season. While this was allowed before, the policy has been changed for the start of the "FIA Gran Turismo Championship 2018 Series," and the manufacturer's affiliation contract will be kept in place until the end of the 2018 season.
The manufacturer's affiliation contract will play a large role in the upcoming championships, so make sure to have a long-term strategy in place when you make your selection. And we hope you keep enjoying Gran Turismo Sport!