Depend of OS.
All DDF provided directly with deCONZ typically reside in
/usr/share/deCONZ/devices/on a Linux system and are loaded first. However, files residing in the home directory of the user running deCONZ (e.g./home/<DECONZUSER>/.local/share/dresden-elektronik/deCONZ/devices) will override the pre-packaged files to allow users to amend and keep their own files if desired.
If you use HA How to add/edit a DDF on Home assistant using text editor?
You just need to create a text file called waht_you_want.json in one folder “devices” with the DDF contain, then restart deconz, and include the device.