I dont know what your live stream is. If it is a camera then you could place a screen within view visible in the corner of your camera view.
There are several topics in this forum discussing display options.
For example this is an interesting discussion ( but use search to find others)
The simplest form would be to include an old mobile phone which does not require a sim. Connect it to your wifi, open a browser or use the Tempest App to display which ever screen you like to view. Mount it near your camera.
Or you could have a large computer screen behind a picture frame displaying any of the display options.
If you want to use data to insert characters within your stream it is going to require more information on your requirements.
cheers Ian 