String Substitution Using Variables in a FOR loop Batch Syntax - string

Question

I am trying to use string substitution to truncate a list of full file paths down to relative paths in an existing text file. In addition there is some basic automated renaming. The renaming works as intended but the string substitution I cannot get to work. All the documentation I could find describing string substitution used standalone strings, not strings stored in variables. So I do not know and cannot figure out the proper syntax. I have also read similar questions asked here and attempted those solutions to no avail.
Everything in my script works as intended except for this line:
SET %%I=%%%I:%Temp_Dir%=%
It does not change %%I at all. The input to the FOR loop %List% is a text file that looks like this:
C:\Users\UserName\AppData\Local\Temp\Batch_Renaming_Temp\Working\out\bin\codesegment.o
C:\Users\UserName\AppData\Local\Temp\Batch_Renaming_Temp\Working\out\bin\graphic.o
C:\Users\UserName\AppData\Local\Temp\Batch_Renaming_Temp\Working\out\bin\helper.o
C:\Users\UserName\AppData\Local\Temp\Batch_Renaming_Temp\Working\out\bin\main.o
C:\Users\UserName\AppData\Local\Temp\Batch_Renaming_Temp\Working\out\bin\game.out
C:\Users\UserName\AppData\Local\Temp\Batch_Renaming_Temp\Working\out\bin
C:\Users\UserName\AppData\Local\Temp\Batch_Renaming_Temp\Working\out
The final output I get right now is identical to the above list.
The desired output should look like this:
\out\bin\codesegment.o
\out\bin\graphic.o
\out\bin\helper.o
\out\bin\main.o
\out\bin\game.out
\out\bin
\out
I know the syntax is supposed to be:
SET string = C:\Users\UserName\AppData\Local\Temp\Batch_Renaming_Temp\Working\out\bin\codesegment.o
SET string = %string:C:\Users\UserName\AppData\Local\Temp\Batch_Renaming_Temp\Working =%
As I said though, I cannot get it to work using variables in a FOR loop. I am also attempting this method of string substitution because the path of %Temp_Dir% is always at the start of every line and is always found in each line once.
Here is the whole script for reference. I would prefer a one line solution like the one I was attempting. I am aware longer solutions are available but due to reasons beyond my control the one-line string substitution is required.
#ECHO OFF
SETLOCAL EnableDelayedExpansion
SET Proj_Dir="C:\Users\UserName\Desktop\Project"
SET Temp_Dir=%temp%\Batch_Renaming_Temp\Working
SET Counter=1
SET List="%temp%\Batch_Renaming_Temp\LFN_LIST.TMP"
SET List_Final="%temp%\Batch_Renaming_Temp\LFN_LIST.TXT"
ROBOCOPY /E /MIR %Proj_Dir% "%Temp_Dir%" > NUL
CD "%Temp_Dir%"
DIR /A-D /O:N /B /S > %List%
DIR /AD /O:N /B /S | SORT /R >> %List%
TYPE NUL > %List_Final%
FOR /F "usebackq tokens=* delims=" %%I IN (%List%) DO (
REN "%%I" !Counter!
SET /A !Counter+=1
SET %%I=%%%I:%Temp_Dir%=%
ECHO %%I >> %List_Final%
)

Answer 1

Like #Squashman pointed out in the comments, you cannot "set" a FOR variable.
If your variable depends on other variables indirectly, you need to use CALL SET or delayed expansion.
The easiest solution so far:
(for /F "usebackq tokens=8* delims=\" %%x in (%List%) do echo \%%y) > %List_Final%
It uses \ as a delimiter and pass the 8+th arguments to %%y, and redirects all output to %List_Final%
Tested on a Windows 10 laptop, works perfectly.