You can change the media by changing the media URL. The URL should be a public link and contain the same type of media. For example, if it is an Image template, then it will only accept PNG and JPEG files.
Users will get the below error when using a media which is not approved, for example, if a user tries to add a video file in an Image template, the below error will be shown
If a user tries to upload a media file that exceeds the size limit, then the below error will be shown.