Use a hook multiple times

we have a multicompany install.
We use 1 module with everything that should run in all entities and 1 module for each entity with more specific customization.

Now I want to use the hook menuLeftMenuItems in both modules.

The function manipulates the array of the menu but when I have both modules running in an entity only 1 modification gets applied.

I am coming from the WordPress world and that hook system is maybe the best there is.
But here I am not able to reverse engineer how the hookmanager tries to run all functions on the hook. Can I set some kind of priority? So the functions run after each other.

Or is there no way to use a hook with multiple actions?

Please help.
I have come across this problem multiple times and always opted to do something dirty.

Cheers.
Chris