I want to install some dependencies on a machine after it created. Have a type of secondary charm, who I could install these dependencies, even if these dependencies do not have a charm in Charm Store?
Juju has a concept of "Subordinate Charms" where you can deploy charms on top of existing deployed services. One such example of this is the Nagios/NRPE charm. Where you deploy the nrpe charm on existing services and relate it to a regular Nagios charm. NRPE sits on top of whatever service it's deployed on and monitors the machine. In this case you can create a subordinate charm to deploy additional services on top of a regular charm.
However, if the charm you're deploying requires these dependencies to work properly it is probably better to fork the charm, add your modifications, then deploy from your forked version.