SOPs when making overrides in WordPress?

We have rewritten the body tag within the embed.php file of HP5 as follows:
<body id="learning-activity-<?php print $content['id']; ?>">
This has allowed us to target and style individual learning modules on an as needs basis via the h5pmods utility.

We would like to make this change persistent in WordPress ie. Regradless of future H5P updates our override remains.
The standard process for overriding a plugin within the WordPress environment appears to be via the themes folder.
Relevant to our  current scenario we have created the following folder structure within the childtheme folder of wordpress,
h5p > h5p-php-library > embed.php which does not appear to work.

Question:  How do we ensure that our override remains persistant regardless of any future updates to H5p in Wordpress?

Thanks in advance, Andy