Unlike site or landing pages, HubSpot's system pages are "global" to the domain they're assigned to. There are also two types of system pages:

Website:

1. 404
2. 500
3. Password prompt
4. Search results

Email

1. Subscription preferences
2. Unsubscribe backup
3. Subscription update confirmation

#1 Website system pages

Here are the steps:

1. Open Content Settings
2. Choose Website > Page
3. Choose the domain you're editing, and click the System Pages tab
   
   
   
4. You'll find the choice fields to update 404, 500, Password prompt, and Search results templates.
   Select each choice field and choose the template you're applying.
   

#2 Email system pages

1. Open Content Settings
2. Choose Marketing > Email
3. Click the Subscriptions tab, and you'll find the choice fields for each of the three email system pages: