How about this one?
Fill inn
source and
target and save the script as
Parts.ahk. Download and install
Autohotkey to run the script.
Skrommel
source=Source.txt
target=Target.txt
#NoEnv
#SingleInstance,Force
SetBatchLines,-1
string:=""
FileRead,lines,%source%
Loop,Parse,lines,`n ; Split by line break
{
StringSplit,part_,A_LoopField,. ; Split by period
If part_0<3 ; 1 part
line:=A_LoopField
Else
StringReplace,line,A_LoopField,%part_1%., ; Remove part 1
line=%line% ; Remove trailing space
string.=line "`n" ; Add line break
}
FileDelete,%target%
FileAppend,%string%,%target%