The function iterates through the input string, skipping every other character, and replacing the skipped character with the next character in the alphabet. It loops 'y' to 'a' and 'z' to 'A' for lowercase and uppercase characters. It preserves numbers and special characters.

[CODE]: 
```python
def modified_function(input_string: str) -> str:
    output_string = ""
    for i in range(len(input_string)):
        if i % 2 == 0:
            output_string += input_string[i]
        else:
            if input_string[i] == 'z':
                output_string += 'A'
            elif input_string[i] == 'Z':
                output_string += 'A'
            elif input_string[i].isalpha():
                output_string += chr(ord(input_string[i]) + 1)
            else:
                output_string += input_string[i]
    return output_string
```