You are able to filter custom fields through members on your site through the Member Directory module.
- Access to a Superuser account.
Once you've created a custom field for the users from Settings > Site Settings > Site Behavior > User Profiles > Add Field.
Don't forget to click Next and set the Field Name to whatever you want to display in the search.
This is an example of a Member Directory module:
Now, if you want to change the terms of Advanced Search you can do it from the module settings:
*Note that the name of the field is the one you used on the second screen while creating the variable.