The MTA official forum explicitly states they do not provide serial change services.
MTA stores a cached version of your serial in a configuration file. Sometimes, simply resetting this file forces the client to re-hash your hardware. Mta Sa How To Change Serial
by the developers. The MTA serial is a unique identifier generated by the game's anti-cheat system based on your specific hardware and software configuration, not just a simple registry key or ID number. Multi Theft Auto Why Serials are Difficult to Change Hardware Binding: The MTA official forum explicitly states they do
The MTA serial is a 32-character hexadecimal string (e.g., F4A3B2C1D5E6F7A8B9C0D1E2F3A4B5C6 ). It is generated by hashing the following components of your system: Mta Sa How To Change Serial