Procedure is near identical. You'll have a service port on the inlet/outlet of the tankless unit to drain. Then you'll blow out the rest of the system like normal.

I have a gas tankless unit in my beecher house. It also supplies hot water for the radiant heat. I love it, it's super efficient and just as quiet as a tank unit. Only downside I've experienced is a slightly longer wait for hot water for washing hands etc. But no issues for multiple back to back showers.