Hello Juang,
Open PADS LAYOUT
Go to "tools\PCB decal editor"
When opened,just go to 2Dlines from librairie
select your template
put it in the windows,modify it
ensure after modifying our templat to recombine all
then select the entire 2Dline shape
Right mouse clic and "save to librairy"
exit décal editor without saving anything else.
you will find now your new template modified next the original in the 2Dline librairie.
Have a good day/Bonne journée.
Vincent.