The ship broker criteria are pretty well fixed at game start and cannot be easily modded. Changing them is also very limited because they can only be replaced.
Possibly some easy way of adding additional criteria could be developed.
I don't have any solid ideas but maybe being able to add a number of different criteria and the game selecting from all of them, including the original.
The ability to easily change total ship numbers would also be good.
Possibly a weighting could be included in each string to allow more of some ships than others based on the strings to be added to the list.
Being able to add a single ship to a station's broker would also be good.
Hat tip to xelerus user @Luna! for the inspiration.