I dont know if this is possible in any way or theres a UI mod for it but i havent heard of that yet.
Imagine you have forgot to build t1 arty and you have 50 t1 tanks but no arty.
so you can just make a usal 1/4 or 1/3 arty to tank build loop with your factories.
but that will take years until you have the arty so the smartest way is to stop your factories and let them each build 5 arties.
when they are finished you have to set up a build loop again, what is pretty annoying and needs micro.
i think it would be really cool if there was a way to set build orders, and queue a loop right after the orders.
for example if you activate the repeat button on a factory, a "|" appears in front of your queue. you can now queue up stuff etc. and move around the line.
when you are finished, everything that is behind the line will be repeated.
so you order 5 arties, click on repeat, move the line behind the arties and then order 4 tanks and 1 arty. the factory will now build 5 arties and then loop 4 tanks + 1 arty.