Is it possible to auto-green up in-play? On Test Mode

I want to put a back bet on at a price that when it is matched, automatically places a laybet on at 10 ticks below that price. I can't seem to do that in-play. What settings do I need to use to do this please? Thanks.

So, for example, when the race is in-play, let's say a runner is at 5.0 odds, I want to place a back bet at 10.0 odds, hoping the price will go up, and be matched at 10.0  When that price is matched, I want Time Machine to automatically place a lay bet 10 ticks below that, that will hopefully be matched.

Yes, sure. Make sure your greenup trigger is set to run in-play.
Have a look at this trigger example.