Live templates expressions: how to decapitalize with underscores?

Hi,

I'm trying to create some live templates following the company code styling and I'd like to have a variable named all lowercase, with underscore.
So something similar to what capitalizeAndUnderscore(<String>) does.

I've tried to use decapitalize(capitalizeAndUnderscore(<String>)), but then I've realized that this only works for the first letter.

How can I do that?