Can I change hotkey combination?

Sure.  The source is included.
Use AutoHotkey from here
to compile.

You have a file selected in File Explorer when hitting the hotkey?

It uses this group:
GroupAdd,ExplorerGroup, ahk_class CabinetWClass
GroupAdd,ExplorerGroup, ahk_class ExploreWClass

with #IfWinActive ahk_group ExplorerGroup

If the active window is anything else, like a third party file manager, the hotkey will not be active.
As a test I would try one that does not use the function keys.  Maybe change it to Control Shift z or something, just to see if that gets a reaction.  Maybe something else is using Shift F11 already.

Well poo.  It was the hotkey combo. That's so frustrating - I tested it before and got no reaction, checked assignments using Ethervane ActiveHotkeys (might be an old version...) and couldn't find any reason why F11 NOR F12 would work.
I changed it to Ctrl+Shift+M and it worked perfectly.
I've since reassigned it to Shift+F10 and Ctrl+F10 and those both seem to work.

Thanks again, sir!

You are most welcome.  Some of my utilities I put in code to allow changing the hotkey via tray icon menu.  But it gets messy handling bail-outs, blanks, the same hotkey is put in as was in effect already etc..  Kind of spaghetti code.

Anyway, glad the program is working for you. 

Quote from: AzureToad on January 27, 2016, 04:00 PM

It was the hotkey combo. ... I ... checked assignments using Ethervane ActiveHotkeys (might be an old version...)

That's not guaranteed to find all used Hotkeys. Apparently some arent registered or something, and show as free even though they aren't. (To clarify: I dont believe it's a flaw of ActiveHotkeys as such, more one of 'the system'.)

Also I think by default AutoHotkey hooks the keyboard and checks the active windows for #IfWinActive type declarations and lets the keys pass if the window is not active or whatnot.  So it would be just about impossible for a utility to detect all the hotkey settings.  My program is a bit of a kludge but it is one way to go if you like using Explorer as file manager and don't want to set up an explicit comment file with a note Tree type program.  I admit it is just a hack.  But Windows does make it tough to do much better without writing your own file manager.