Hello!
So we don't really support this out of the box. In the category we set labelSpan.textContent='nameYouPassedIn'. I think the fact that we use textContent is the reason why using <br> does not work.
toolboxLabel.appendChild(firstHalfOfWord);
toolboxLabel.appendChild(document.createElement('br'))
toolboxLabel.appendChild(secondHalfOfWord);
Hope that helps and let me know if you have any other questions!
Cheers,
Abby