First of all, you shouldn’t edit the plugin code directly, all your changes will be vanished once you update the plugin. If you have edit the plugin code, please check it with new activity uploads. BuddyPress stores activity content into database so once activity content generated you can’t change them by just changing plugin code, you have to check it with new uploads.
Other solution I cant think of is to use
rtmedia_bp_activity_posted action hook and change activity content using regex and string search/replace to alter the markup of content. You just need to search for
rtmedia-activity-text class and extract that div from markup and append it at the end of markup. You can check about the hook here: https://github.com/rtCamp/rtMedia/blob/3.8.21/app/main/controllers/activity/RTMediaBuddyPressActivity.php#L141