It is possible for you to bring a car from your single player game into GTA Online even after the latest update — you just can't do it with DLC cars or with cars labeled as "too hot."
Follow the steps below to bring any other car into GTA Online:
- First, drive the car to any Los Santos Customs location.
- Save your game.
- Drive it into Los Santos Customs.
- Pause the game and choose to enter an Invite Only Session of GTA Online.
- From there, pause again and choose to host a Job.
- Pick a race.
- Complete the race.
- Rate the race.
- Quit out of the "Vote on the next Job" screen, which should make you spawn in Los Santos Customs in the car you drove there, even though you're still online.
- Either sell the car or take it to your garage.
- Switch back to single player to repeat the process if you would like to bring more cars into GTA Online.