Yes. Please see: Customizing Pro-Forms

100% Optional; Pro-Forms Integrate w/ WordPress Shortcodes

Customizing Pro-Form template files is usually NOT necessary, because Pro-Forms inherit styles introduced by a WordPress theme of your choosing. Pro-Forms come fully functional. They work as-is in most WordPress themes. If you need to tweak their appearance, most site owners accomplish this through custom CSS alone. Again, modification of Pro-Form templates is not necessary in most cases.

Customizable PHP Template Files for All Pro-Forms Advanced

With the above in mind, if you'd like to create custom Pro-Form templates, please check your /s2member-pro/includes/templates/forms/ directory. You can take s2Member's default Pro-Form templates, and place some (or all of them) into your own WordPress theme directory. By placing custom templates into your active WordPress theme directory, you can be sure they won't get overwritten in a future upgrade of s2Member. s2Member will automatically detect the presence of your custom template files, using those instead of its default templates.

Tip: Custom template files can also be placed inside of your /wp-content/ directory. s2Member will find them there also.