Hi Zuhnja,
You can use URL Parameter "sap-ui-application=any/js/module" which will perform a require on that js during load time *as long your Fiori Launchpad does not have a rootComponentNode assigned in its config*.
The main thing for you is to have a module path registered at that time or add a new class in one of the ones declared in Fiori Launchpad, the bootstrap methods will do a require and a new() on that file and you can pretty much also listen to the same event I posted (the core will be booted and ready) to have your custom logic executed after the launchpad is rendered, so you can append your own nodes in the DOM.
Hope it helps,
Dan.