XYplorer Beta Club

I'm finding that as my laptop is getting older and, lately especially, really, really slowing down, that I'm using keyboard shortcuts more than ever esp. as they get me almost back to regular speed despite the loss of speed.

I was trying to get the tabs in XYplorer to work more like my browser's but when I try to change MOVE TAB TO LEFT with Ctrl+Shift+PageUp and MOVE TAB TO RIGHT with Ctrl+Shift+PageDown, that I can't seem to customize to those two key combinations. Some red text comes up in the customize keyboard shortcuts editor for both that says:

"This shortcut is not customizable."

Why, please? And is there no way to get around this? I really need to be able to move tabs with these shortcut keys as they're what I'm used to, and also because I can't change these 2 key combinations in my browser. I've googled and searched through the forum here but nothing pertinent comes up.

Thank you.

These combinations are hard-coded as traditional shortcuts for multi-selection in many programs dealing with lists. Because of that, I think. Tabbed browser is another case.
What about Ctrl+Shift+[ and Ctrl+Shift+]?