Custom messages for user_pass_reset
If you mean the email message for a password reset. You can use hook_mail_alter to change the email contents before it's sent out to the user.

If you mean the form the user sees on the webpage, then you can use hook_form_alter to change the verbiage shown on the screen.

Edit

override the displayed form with the reset button to goto your own form_submit action. In your custom module action, simply copy and paste user_pass_reset function body into your own function and tweak it as needed to change the messages (careful).