addDate.sh

#!/bin/bash
#put in $HOME/bin/

OIFS=$IFS
NOW=$(date +"%y%m%d")
IFS='.' read -r -a array <<< $1

for result in "${array[@]}"; do
    echo $result
done

echo ${array[0]}
echo ${array[1]}

mv $1 ${array[0]}_$NOW.${array[1]}

IFS=$OIFS

miscfiles.desktop

#put in ~.local/share/kservices5/ServiceMenus/
[Desktop Entry]
Type=Service
# all files inherit from application/octet-stream
MimeType=application/octet-stream;
X-KDE-ServiceTypes=KonqPopupMenu/Plugin
X-KDE-Submenu=MiscFiles
Actions=addDate

[Desktop Action addDate]
Name=Add Date
Name[sv]=Add Date
Icon=utilities-terminal
Exec=$HOME/bin/addDate.sh %f