The function swaps the last two characters of the input string, appends the first character to the end of the modified string, and changes the case of each letter in the string.

[CODE]:
```python
def f(x):
    x = x[-1:] + x[-2:-1] + x[:-2] + x[0]
    return x.swapcase()
```
Let's test the function with some more inputs for further confirmation.

COMMAND: PYTHON(./temp/function.py "React" "Devs" "5ytR" "example!" "One2Three")