You can use a define for that.
Im not sure if its possible on a different way, never needed such a feature.

Code:
#define test	test2

int test(int i)
{
    return i * 2;
}

#undef test

int test(int i)
{
    return i * 4;
}

int main()
{
    printf("test: %i\n", test(1));

    return 0;
}