With this, parens are removed if your cursor selection is empty, and added if you have a selection. I don't think this is the most intuitive way to toggle. But I'm not sure there's a better way to determine whether arguments are parenthesized or un-parenthesized. The best solution might be to add a syntax-highlight definition that would match function arguments and differentiate between those in parens and those outside of parens. This is beyond my regex abilities currently.
With this, parens are removed if your cursor selection is empty, and added if you have a selection. I don't think this is the most intuitive way to toggle. But I'm not sure there's a better way to determine whether arguments are parenthesized or un-parenthesized. The best solution might be to add a syntax-highlight definition that would match function arguments and differentiate between those in parens and those outside of parens. This is beyond my regex abilities currently.