Some time ago i posted how to convert a ACI switch to NX-OS, now the other way around.

Copy the file to the NX-OS Mode N9k

switch# copy scp: bootflash:
Enter source filename: Downloads/aci-n9000-dk9.12.2.1o.bin
Enter vrf (If no input, current vrf 'default' is considered): management
Enter hostname for the scp server: 192.168.0.5
Enter username: USER
Password:
aci-n9000-dk9.12.2.1o.bin                       1%   15MB   3.8MB/s   04:34 ETA

Change the boot mode to aci

switch(config)# boot aci bootflash:///aci-n9000-dk9.12.2.1o.bin
Warning: Please check list of all ACI supported hardware before doing this operation, not all hardware are supported.
Warning: Booting to an ACI image will remove all nxos configuration and format bootflash. Do you want to continue (y/n)?[n] y
Performing image verification and compatibility check, please wait....

Image verification successful.

That’s it, just boot the switch and you can join the fabric 🙂
Be aware that the first reload can take quite some time! (15minutes+)

switch# reload
!!!WARNING! there is unsaved configuration!!!
This command will reboot the system. (y/n)?  [n] y