You can change the profile data used in your email templates in the visual editor.
In the template you want to edit, select the Preview tab and scroll down to Edit profile data used for rendering template.
Define the attributes of the intended recipient to preview the template for a specific contact segment:
Depending on the profile data you select, the preview window will display the blocks visible to these contacts.
This is useful for previewing your dynamic blocks.
Click Edit raw to see the profile data (for developers).