(Kubuntu 18.04, KDE Plasma 5.12.9)
I'd like to try Krusader in place of Dolphin and would like to continue using Meta+E as the keyboard shortcut. After installing Krusader, I did the following:
I opened System Settings from the application menu.
I looked under the Workspace heading, clicked Shortcuts -> Global Shortcuts -> KDE Daemon and found the entry File Manager: Meta+E. I made no changes here.
Back in the main window of System Settings, under the Personalization heading I went into Applications -> Default Applications -> File Manager.
I selected the radio button Other: click Add... in the dialog shown here and clicked the ... button next to it.
I was presented a dialog box entitled Edit File Type inode/directory -- File Type Editor. In the lower panel entitled Application Preference Order I clicked the Add button.
I was presented a dialog box entitled Choose Application for inode/directory -- File Type Editor with the a tree listing of application categories found in my application launcher. I selected Utilities -> Krusader, which added Krusader at the top of the list of applications in the Application Preference Order panel.
I clicked OK, there was a dialog box that gave an indication that something was being updated. When done, in the File Manager -> Default Component list I selected Krusader and clicked Apply.
As it was in the KDE Daemon category, not knowing how to restart a daemon without rebooting the computer, I went ahead and rebooted.
Unfortunately, Meta+E is still bringing up Dolphin. I did discover, though, when right-clicking an empty spot on the desktop, the context menu has an entry, Open with Krusader Alt+D,T which does work. I don't know where this shortcut is defined. I can use that in a pinch, but would prefer Meta+E. Any suggestions?