The function replaces the second character of the input string with 'k', and replaces the last character with the letter that is immediately before it in the alphabet.

[CODE]: 
```python
def approx_function(s):
    s = list(s)
    s[1] = 'k'
    s[-1] = chr(ord(s[-1]) - 1)
    return ''.join(s)
```

To make sure the approximating code works, let's run it on a few more inputs.

COMMAND: PYTHON(./temp/function.py "instruction" "algorithm" "coding" "snippet")