A message is shown upon successful registration, with the following contents:
A welcome message with further instructions has been sent to your e-mail address
I would like to change the content of that message and use a different HTML structure, e.g.:
<p>Thanks for registering</p>
<a href="#">continue</a>
How can I do that?
you can achive this and much more similar things with LoginToboggan module, from module page:
The LoginToboggan module offers several modifications of the Drupal login system in an external module by offering the following features and usability improvements: Allow users to login using either their username OR their e-mail address. Allow users to login immediately. Provide a login form on Access Denied pages for non-logged-in (anonymous) users. The module provides two login block options: One uses JavaScript to display the form within the block immediately upon clicking "log in". The other brings the user to a separate page, but returns the user to their original page upon login. Customize the registration form with two e-mail fields to ensure accuracy. Optionally redirect the user to a specific page when using the 'immediate login' feature. Optionally redirect the user to a specific page upon validation of their e-mail address. Optionally display a user message indicating a successful login. Optionally combine both the login and registration form on one page. Optionally have unvalidated users purged from the system at a pre-defined interval (please read the CAVEATS section of INSTALL.txt for important information on configuring this feature!). Integrates with Rules module to do various tasks when a user validates via email validation process (see http://drupal.org/node/880904 for an example)
UI settings are simple and straight forward, and are located in admin/config/people/accounts
