Mandlazi was also denied bail.
He was driving the truck when it collided with a coal train between Hectorspruit and Malalane on Friday morning. He was initially charged with culpable homicide, and then murder, but the charges were reduced to culpable homicide during his first court appearance on Monday.
On Tuesday, they were again changed to murder.
"His case has been changed back to murder after police came forward with strong evidence of what happened before the accident," said provincial police spokesperson Colonel Leonard Hlathi.
Mandlazi was not asked to plead and was remanded in custody until 14 August.
Investigating officer Lieutenant Senzo Banda asked the court to deny Mandlazi bail for his own protection because the community was still angry. He also said arrangements were being made to give him counselling.
Mpumalanga MEC for Community Safety, Security and Liaison Vusi Shongwe said the farm owner would also be questioned in connection with the incident.
"The farm owner will have something to answer for in terms of labour laws," he said.
The farmworkers were on their way to harvest oranges at Tulloh citrus farm when the accident happened.
Meanwhile, the department's spokesperson Joseph Mabuza said two of the victims had not been identified yet.
"There are two bodies that have not yet been identified and we are calling for people who had relatives working at Tulloh farm to come identify them," said Mabuza.
He added that the Nkomazi local municipality had opened a trust account to raise funds to help the bereaved and destitute families.
"All these families are poor. They can't afford a funeral and food, and in some families the deceased were the only working people, so every bit of help can go a long way," said Mabuza.
The Road Accident Fund has also undertaken to help bury the victims.
A memorial service will be held on Thursday while a mass funeral service will take place at KaMhlushwa stadium on Saturday.
The trust account for those who wish to make donations is: Bereavement Fund, ABSA branch code 632005, account number 4078501159.
