IAS is open to Indian citizens only, by writing IAS exam while being a US citizen is not recommended. OCI is unfortunately only a visa category, not a citizenship. OCI living in India for 5 years bexomes eligible to apply for Indian citizenship, not an automatic process.
Consult an attorney who specializes in criminal as well as immigration laws in India; Indian laws may be different when treating a candidate who fradulantly claims to be an Indian citizen. good luck!
IAS is Indian Adminstrative Services (civil services), IAS officers may potentially impact/create policies that impact how state/federal government operates.
Note : I am not a lawyer, Please don't treat my messages or posts as legal advise.