I would like to modify the DietPi first run setup to not repartition the drive. There are other partitions with data that must be maintained. I’m considering replacing our current Debian image with DietPi.
Do you mean the resizing of the partition?
https://github.com/MichaIng/DietPi/blob/063b3b62d942f5be9297166293d429370a941d2f/rootfs/var/lib/dietpi/services/fs_partition_resize.sh
You could just clone/fork the repo, modify to your needs and build your own images.
would be good to have some more information on current scenario and what exactly should be done.