Having changed the question set, how do I ensure the link that I've sent to the client is using the right selection?

The link sent will only include the question set you had selected just before you generated the link. If you need to change it after you've generated the link, you'll need to generate a new link which you can do by selecting the download version radio button, then selecting the generate link radio button and making your choice of question sets again before clicking "generate secure link".

We recommend completing some initial checks/changes with a test client before using the Client profile area with your clients.