Which corresponding global settings file do you need to modify?

[haohaohao]

What about creating a custom charset?

Something like this:
--custom-charset1=?d?l?u!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~

?d are digits, ?l are lower case characters and ?u are capital characters. Just leave out the special characters in my example.

When I want to use ?a, I want to get rid of the unusual special symbols.