AWS won’t let you copy default RDS parameter groups.
If you want to customise parameters, you need to create a new parameter group in the same family and tweak it from there.
Default parameter groups are locked—you can’t edit or duplicate them.
To make changes, you need to create a new custom parameter group within the same family (e.g: postgres9.4).
The new group starts with the default settings, and then from there you can modify what you need.
Not automatic - You have to manually associate your RDS instance with the new parameter group once you’re done editing.
Some changes need a reboot - Certain parameters only apply after a restart, which means you need to plan for downtime.
It’s makes sens to apply changes during a maintenance window to avoid surprises.