After you have shared a link out, you can still make changes to it settings without having to resend or create a new one.
To do so, select the bar chart icon on the lefthand side for "Reporting." This will show a history of your previously sent links. Administrators will see all links from all users across the account.
Select the ellipsis to the right of the link you desire to edit and select "Edit." This will reopen the share modal to modify settings:
Add Files to Existing Link:
In this Share window, you can also add assets to a link that was already shared. Click the "Files" tab next to Link.
In the top right of the window, click on the "Add" button which will open a Media Browser to search for assets you may want to add to the link across different projects.
Once you have added a new asset, it will update the link you shared for the recipient without having to send a new one.