Well.....All it took was a day to get stuck...
At first, I thought I had it, I went through the Properties and found which ones changed when I turned on the scenario I wanted to include. I came across /sim/ai/scenario[1], the value being the scenario name (in this case, Alpha_1) which came and left when I was switching the scenario on and off. I thought "Great, thats it! Just refer to that In the set tag under step and that'll do it!"
How wrong I was.....
It turns out that that property was JUST the marker in the box appearing and disappearing. In other words, /sim/ai/scenario[1] is just the marker in the box.
Start again....
I have tried a few things since: I have tried to find any other properties that appear and disappear during the switching on/off of the scenario. I found /ai/models/tanker was coming and going as well. (I will say I was playing around with a tanker) So again, "Fine, lets just refer to /ai/models/tanker in the set tag under property...." but what was the value? there wasn't one, just a load of properties and values under /tanker. It could've been any one of them! So what I did was try and put all of the properties and values under separate set, Property and value tags in the tutorial xml. Did that work? No. although I did notice that when I made the list of properties in the tutorial xml, and activated it, most of the property values in the property branch had "(string)" behind them, whereas when activating the scenario manually in game, some had "(bool) standing for boolean? Perhaps that's why its not working?
I finally tried to load an aircraft model in outside the step tag and then find some form of speed/rpm property to refer to. there were none. I tried to make one in the tutorial xml, but it didn't work.
So i've tried a few things and am still trying to get my head around it. Clearly you can't make a model move in game as there is no allocated tag for it (A chance to get developers to make one?) and I can't find a property to refer to when It comes to activating a scenario. I thought activating the marker in the box would work but somehow it doesn't. Maybe I have to refer to the marker in the box appearing, in the scenario xml to activate it?
...Any thoughts?
(to anyone reading, this is of a course a branch off from a separate discussion, "Pop up messages in Scenario")