Is it possible to pass significant data types by reference?

Yes, it is possible using the ref or in keywords.

Example with ref (for read and write):

void ModifyValue(ref int number)
{
    number = number * 2;
}

// Usage
int myNumber = 10;
ModifyValue(ref myNumber); // myNumber is now 20

Example with in (read-only, for performance optimization when passing large structs):

void ReadValue(in MyStruct data)
{
    Console.WriteLine(data.Value);
    // data.Value = 10; // Compilation error, in makes the parameter readonly
}

struct MyStruct
{
    public int Value;
}

// Usage
MyStruct myStruct = new MyStruct { Value = 5 };
ReadValue(in myStruct);

Example with out (for initialization inside the method):

void CreateValue(out int result)
{
    result = 100;
    // Console.WriteLine(result); // Compilation error, can be used only after assignment
}

// Usage
int outputValue;
CreateValue(out outputValue); // outputValue is now 100