Why do you do it that way? Why not just use the values or set the variables to the values prior?

But regardless, you can use Quiet. If you explain why you're doing it that way, I could come up with better suggestions.

Thanks, Eric.

The motive for the question was that it's easier to change variable values with a ReplaceAll[] at the end of a function than to enter values directly when experimenting with different values. That's especially true if the same variable is used more than once. In trying to focus my question narrowly, I oversimplified by using an example where the variable was used only once.

My problem with the Quiet[] solution is that I don't want to silence the error when there really is an inappropriate argument.

The predefined variables idea is a good suggestion. I often do that. But if I'm doing different things in in different parts of a notebook, I can make problems for myself by defining too many variables. I could include a Clear[] in the cell after the function to solve that problem. Maybe that's the best way to solve the problem without creating many variables in a notebook. I infer from your post that the answer might not be as simple as I hoped when I posted the question.