Yes you can! It is possible to make use of the return key in large (more than one rule) text fields in clips.
You should however keep in mind that every clips has a maximum number of lines available to write on. Using a return will shorten this maximum with one line. The system does not anticipate on returns, so your remaining characters will be reduced by one, instead of the whole line. Therefore you must be aware that by using returns, fewer characters than the remaining characters are available for you to write in. This can result in text that is not displayed on screen. If you don’t use returns, the remaining characters show the correct amount and everything will be visible on screen.