The function takes an input string, swaps the second and third characters, and appends "GOBo" to the end of the modified string.

[CODE]:
```python
def approx_function(input_str):
    input_str = list(input_str)
    if len(input_str) >= 3:
        input_str[1], input_str[2] = input_str[2], input_str[1]
    return ''.join(input_str) + "GOBo"
```

To further confirm its behavior, we can run more test cases.

COMMAND: PYTHON(./temp/function.py "ABCD" "abcdef" "1a2b3c" "x4yz8" "-=>")