You can set a role that applies to all properties in a portfolio by default by setting the role at portfolio level. To do this, go to properties list and click on the pencil icon to the right of the portfolio name.
This will display the portfolio settings page. From here, click the ADD NEW ROLE button to display the role and contact selector.
Choose the contact and the appropriate role, then click SAVE.
In the example above, Mark Sorsa-Leslie will be set as the the Surveyor role for all properties in the portfolio by default. Adding Mark at the Portfolio level means that, in future, to change the surveyor for the all the portfolio simply requires an edit of the role at portfolio level.
Please note that if a role is added at the Portfolio level and also at the Property level, the Property level role takes precedence over the Portfolio level role and will remove the default value set at portfolio level.