In the Standard shader, can I add an extra texture that will not affect the main texture?

I'm working on a system that uses a virtual texture to store data on a surface, that matches the exact UV coordinates of the actual texture being used on that surface. Is there a texture field in the Standard shader that is ignored in certain circumstances? For example, if I add a Metallic texture will it be ignored if the Metallic value is set to zero (and will setting that to zero affect the main Albedo texture)?

Edit: It looks like I can use the Detail Mask as long as I don't use the Secondary Maps (Detail Albedo x2)