I have not posted anything to this thread till now because I simply can't understand what is the benefit pressing the 2 keys Shift+Tab instead of Backspace twice. I personally think that pressing the Backspace key twice is faster because easier to press than Shift+Tab.
However, the indent spaces can be also removed without a find/replace. But the solution would be extremly slow, because you have to copy the selected text into a new file, use a loop which removes the fixed number of indent spaces at very line of the text, selects the modified text, copies it, closes the new file and pastes it over the still selected text.
The macro code for unindenting a single line is available at Is there any shortcut to unindent a single line
Also this solution has 2 problems. It works only for a fixed number of indent spaces and not tabs, if you do not write a better macro as the one mentioned above. And since UE v12.10+3 it will not really work because of the new focus handling when closing a file described at Problem with Previous Window/Tab Command
, if you have more than 1 file open and your file is not the most right one in the open tab sequence.