Hey @davidecavestro.
So, if I am understanding you correctly, you are looking for something that would be akin to global variables or a global Set node where you could set different parameters which could be referenced outside of the workflow.
I know you referenced this in your initial post, but using a Set node such as this:
with the following workflow:
by directly referencing the values set in the Global Config node.
I know that this is not the answer you are looking for but it does provide the required results with the system as it stands today.
The only other way to do this would be for n8n to be rewritten at a base level with another section, as you put it, like the credentials section. If that is the case, my recommendation to you would be to then submit an enhancement request so that the developers could put it into the work and prioritization queue.