Thanks @saguaros. That was easier than I thought. For others wanting to do the same, you need to edit file:
/templates/ja_vital/acm/video/templ/style-1.php
Change line 28 from: <a id="myvideo-<?php echo $mod; ?>" class="html5lightbox bg-primary" data-group="myvideo" href="https://www.youtube.com/watch?v=<?php echo$helper->get('id-video'); ?>" title="">
to new: <a id="myvideo-<?php echo $mod; ?>" class="html5lightbox bg-primary" data-group="myvideo" href="https://player.vimeo.com/video/ENTERVIMEOVIDEOID/<?php echo$helper->get('id-video'); ?>" title="">
Obviously, replace ENTERVIMEOVIDEOID with the id of your video
In the module itself, you need to include something in the Youtube Video ID field (or the play button will fail to display in front-end) where I've included: ?autoplay=1
Save both the .php edit and module, clear cache in browser and it should work without issue. An alternate way to do this, and arguably a better solution, would be to use the line href="https://player.vimeo.com/video/
and just include your VIDEO ID in the module itself eg no need to include ?autoplay=1
Thanks again