Yes it is, a small modification would enable you to call the function with a certain parameter about the maxsize, and set the function to return True/False if a (sub-)folder is found larger than that.

Depends on what exactly you want to do... you could replace the line where it prints the foldername, and use that to set the function's returnvalue to true. Remember to set the initial value to false and also flag the first call of the function as it is recursive ...

if you need help, send me a msg, i'll modify the code for you..

I must say that what you are suggesting is not really effective, users will quickly learn to ignore such warnings. You could perform some more rigorous actions instead of the warning, possibly log to a central file or mail something to somebody. But then again, you could also just run the function over all your userdirs every now and then. It all depends on the situation..