How to I prevent shortcrust cracking while using a tartet machine?
Your shortcrust is a bit low on liquids. Here's why:


Icing sugar is more hygroscopic than regular sugar. This is generally good because helps in making water unavailable for gluten formation, but since there's a lot of it, it won't be 
There isn't a lot of margarine
Assuming your eggs are in the 50g - 60g range, 240g of eggs is a bit on the low side.


There are also a few unclear things:  


What is the exact weight of the eggs? You should weigh them!
Are you letting the dough rest in the fridge before using it? It should rest at least a couple of hours, ideally 12-24 hours.
How are you making the dough come together? Are you using a stand mixer, your hands, a spatula, a food processor?
In what order are you mixing the ingredients?
When are the cracks appearing? During the cooking process?


Since you can't change the ingredients, I would try adding another egg. It would add both liquids and color, and the dough should come together much better.

Color could improve vastly by using only yolks, and possibly by switching to a different egg vendor with more orange yolks. This would require rebalancing the entire recipe though.

Regarding the color, I have no experience in using a tartlet machine, but 165 °C seems low, and 115 °C seems very low. I would try higher temperatures (without exceeding 180 °C), keeping the time the same.

While not strictly related to the issues at hand, you should also really reconsider the high protein flour: it has no place in a shortcrust, which should use the lowest protein flour you can find.