I believe, you can set the power options so it will not turn the TV off when switching activities.
Yes you can not call the same activity. I programmed mine so it would volume up twice during each time I activated it.
So for example:
I would tell Alexa (or push button in smartthings) Turn on "make louder"
Harmony would switch to that activity, volume would go up by 2.
Core would see the “make Louder” activity ON.
Immediately switch back to TV activity with no intervention.
If it wasn’t loud enough I would do it again.
This was a while ago, so not sure if it still works? Just know this is what I did. Now Alexa has the ability to change volume so I probably could remove this.
I do not watch / use the TV much. I recently got the hub and really haven’t finished setting it up. (Work and all). My wife uses the TV 90% of the time. She still just grabs the remote. She has issues getting Alexa to do things for her. So she just avoids that route. (Usually operator error, not Alexa itself)