Can I add a custom relationship type for a contact who has more than one role with a client?

No, you can only assign Engager's existing, built-in relationship types to a contact. There's no option to create a custom one.

The built-in types are Company secretary, Director, PSC (Person of Significant Control) and Shareholder. One person can hold several of these for the same client, so a contact with more than one role can have each of their roles added.

If you need a custom type, submit it as a feature request using Tell us what to build next in the in-app Need help? panel.