From List.TXT To Separated Number.TXT or Viceversa BAT CODE

Create (From List.TXT to separated nunber.TXT files):
@echo off
setlocal enabledelayedexpansion

set /a count=0

for /F "tokens=*" %%A in (List.txt) do (
    echo %%A > !count!.txt
    set /a count+=1
)

Merge (From  separated nunber.TXT files to List.TXT)
@echo off
setlocal enabledelayedexpansion
set "outputFile=List.txt"
set "separator= "
for %%f in (*.txt) do (
    if not "%%f"=="%outputFile%" (
        set /p line=<"%%f"
        echo !line!!separator!>>"%outputFile%"
    )
)

Delete all TXT files:
@echo off
del *.txt