Do you really need to watch the stream as a channel, or do you just need to watch it? if it doesn’t matter how, then it’s very easy to watch any stream through the MPV plugin, just feed it a playlist.
At the end my final setup would be, that I have several IPTV channels, all targeting the same HDMI source, but I want to execute some scripts depending on which IPTV channel is chosen to make some adjustments. Plus I want to record the stream of the HDMI input. So yes, somehow I need channels in VDR to distinguish the setups and be able to record it via the VDR mechanisms.