Try like this :
@echo off
set "$DelVar=Union"
set "$File=test.txt"
if exist Output.txt del Output.txt
for /f %%a in ('Find /V /C "" ^< %$File%') do set "$Nbligne=%%a"
setlocal enabledelayedexpansion
set "$c=1"
for /f "delims=" %%a in (%$File%) do (
set "$Line=%%a"
if !$c!==%$Nbligne% (
set "$last=%%a"
set "$Last=!$Last:%$DelVar%=!"
echo !$Last!>>output.txt
exit/b
)
echo !$Line!>>output.txt
set /a $c+=1
)
It will create a file Output.txt without the word Union of the last line.
You can set the word to remove in the Variable $DelVar
and the file to check in $File