Dynamically Change Logging Level of a Python Process
Logger.setLevel() is the right way to dynamically change the logging level of a Logger object. Your script will work fine.

I'll nitpick:


Code is read from top to bottom. You should place the comments above the group of statements they are attached to, not below them. If the reader reads the comment first, they won't have to spend extra effort to decipher the meaning of the following lines, because they have read the annotation first.
Be wary of using asynchronous signal handlers when you are using the logging module. I know that this is a tiny example script, but always refer to the documentation when you are using the Python standard library.