The function takes a string as input and returns a new string with the following modifications:
1. Replace each character in the input string with the character 1 position before it in the alphabet. For example, b becomes a, c becomes b, etc.
2. Append '2' to the modified string.
3. Lastly, add the character 1 position after the first character of the input string. For example, 'a' adds 'b', 'b' adds 'c', etc.

[CODE]: 
```python
def function(s):
    modified = ''.join(chr(ord(c) - 1) for c in s)
    return modified + '2' + chr(ord(s[0]) + 1)
```

Please note that this is an approximation of the behavior of the provided function. There might be minor inconsistencies, especially when dealing with input strings containing special characters or numbers.