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What do you mean by “only in specific categories”? Should the names simply not be displayed in some categories, or should they really only be visible in some categories and not be displayed anywhere else, like, for example, in the profile?
Is it more about hiding the name so it won’t be displayed, or about protecting it from being discovered under any circumstances?
If it’s about security, you will probably need a plugin; otherwise, a theme component might be enough.