Here's how to add custom IDs to your contacts:
1. Go to your Network.
2. Click the ... option on the contact you wish to add an ID to and click the Edit contact option.
3. In the Custom IDs field, start typing an ID. If the ID you type doesn't already exist, you will be given the option to create a new ID.
4. You can add as many IDs as you wish. After you've added all the IDs you want, make sure to save your changes.
If you add an ID that already exists for another contact, you will receive an error and won't be able to save the contact.