OK, I found this You Tube video most helpful in removing the Air Box, etc.
Re special tools, You will need LARGE Pliers especially the very large Hose spring clip on the airbox. If the spring clips on the hoses look really badly corroded, you may want a spare jubilee clip or 2 incase they break when you try to open them.
I found it easier to remove the Thermostat and its attached hoses as one unit off the DSG Cooler, and then undo and replace the Thermostat unit on the workbench.
Loss of fluid this way is less than a cupful. You will need to slowly prise off the hoses from the metal DSG cooler fittings, once you have moved the clips back onto the middle of the hose. I used a wide flat bladed screwdriver.
Now to the Thermostat itself. Yes there are many available at different prices, and that is because they all have different Temperature opening settings. You tend to find that the cheaper units have a lower opening Temp, as they are for other VAG models, that require different opening Temps in the DSG cooler.
For the DSG on the Yeti, you want an opening Temp of 75.C not any lower, Else Consumption, smoothness of gear change, etc will be effected,