Modifying a vehicle without RTO permission is illegal in India and can lead to registration cancellation. The Supreme Court has ruled that the structural details of a vehicle cannot be altered from its original manufacturer specifications.

What is permitted with RTO approval:
- Color change of the vehicle body.
- Installation of CNG/LPG fuel kits.
- Engine replacement of the same make and capacity.
- Fitting handicap-adaptive controls.

Process for Alteration Approval:
Apply in writing to the RTO before making modifications. Once the RTO issues permission, get the alterations done at an authorized workshop. Submit Form 22C and Form 22D along with original bills and certificates to get the changes updated in the RC.