I'm wondering if UMl dependencies can be customised ? For example if I have the following 2 layers and I need a specific communication between both of them.
Am I allowed to design it this way? Because I've looked into all sort of dependencies that UML provide and I didn't find a suitable one for what I need:
This is valid. What you did is naming the connector. And of course any human can detect the associated semantics you want to communicate.
A better way of doing that would be to create a Profile (see pp. 250 of UML 2.5). This allows to define stereotypes for UML elements (which also include connectors). Along with the profile you should have a documentation that explains the semantics of every stereotype defined. It is also possible to define custom rendering for stereotyped elements.