I have figured this on my own and I will share it here how as the support team might be too overloaded to think all the ways to approach this for every customer .
So I got the art backup file , let’s call it " originalart.bin" and then I went in console thru UART and did the following :
- type “cat /proc/mtd/” to look for the partition name ( in my case mtd6 )
- make a backup of it just in case ( though not much point for me but still) “dd if=/dev/mtd6 of=/tmp/art.backup”
- SCP in the router and save the backup locally on a computer
- uploaded thru SCP to /tmp/ the file i got from support “originalart.bin”
- went into the router UI thru a browser and installed from Applications->Plug-ins the plugin kmod-mtd-rw ( might need to update the repo before you can find it)
- Went into UART console and typed “insmod mtd-rw.ko i_want_a_brick=1”
- still in console typed " mtd -r write /tmp/originalart.bin art"
- the router flashed the ART partition and then rebooted
- Now all the details are correct but a full restore to factory setting also will restore the network name and all the other bits.
The guide is based on [OpenWrt Wiki] How to restore ART partition and there are other ways of doing this from uboot also but I just went the lazy way on this one.
Anyway lots of fun and learning during the process and thank you again to alzhao and @Johnex for each ones tips and support during this process 
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L.E.: some grammar edits .