Nexus3 custom container image creation | changes missing

I needed to modify the default container image ```
sonatype/nexus3


nexus.properties

How to do I create a custom image after copying the files to the mounts in the container 

**Below are the mounts available in the container:** 
Filesystem               1K-blocks     Used Available Use% Mounted on
overlay                   20961280  2973424  17987856  15% /
tmpfs                        65536        0     65536   0% /dev
/dev/mapper/rhel-lv_root  20961280 13248920   7712360  64% /nexus-data
tmpfs                      8200228   108500   8091728   2% /etc/hosts
shm                          64000        0     64000   0% /dev/shm
tmpfs                      8200228        0   8200228   0% /sys/fs/cgroup
tmpfs                      8200228        0   8200228   0% /proc/acpi
tmpfs                      8200228        0   8200228   0% /proc/scsi
tmpfs                      8200228        0   8200228   0% /sys/firmware
tmpfs                      8200228        0   8200228   0% /sys/dev/block

I tried creating a custom image after copying the file to the above path, however the newly created image does not have the config file. My assumption is that the mounts in the container are not persistent. 

Could someone guide me on the above ? 

Thanks!