Hi Eray,
When generating C code from a Simulink model that includes a MATLAB Function block, the code generation process may rename local parameters used within the MATLAB Function block. This behavior is expected and is done to ensure the generated C code is valid and does not conflict with any existing variable names.
If you have any concerns about the renaming of parameters or if it is causing issues with your code, you can consider using input and output arguments for your MATLAB Function block instead of relying on local parameters. This will case the parameter names to be preserved in the generated code.