Good news, I have updated my brand new SSA3021X Plus to an SVA1032X, I did a couple of things slightly differently though.
When I first got the unit I used the ALL code and 3032 code to fully option it as an SSA3032X Plus.
As my unit came flashed with 3.2.2.6.0R1 I had to downgrade first to 3.2.2.5.1R1, BEFORE downgrading i changed the system setting to have it turn on with default settings not "last used", in case it caused problems as I have read that it can cause trouble on devices when doing updates, I then flashed it and that worked fine.
Before installing the cross flashed SVA firmware I copied over the na_1p and na_2p files, I then rebooted and then I flashed it with those already in place (just in case I couldn't get back in with telnet)
After flashing with the SVA cross flash I did the ALL, and 3032 option codes, but still had the model showing as a SSA3032X Plus, then I did another telnet backup, and copied over the NSP file to update the model name using telnet as below:
mount -o remount,rw /usr/bin/siglent/firmdata0
cp /usr/bin/siglent/usr/mass_storage/U-disk0/SA-firmdata0/NSP_trends_config_info.xml /usr/bin/siglent/firmdata0/NSP_trends_config_info.xml
Once I did that I updated to the latest firmware 3.2.2.6.0R7
So far all looks perfect, my serial number is intact, I have the correct model name, and seemingly the VNA functions appear to be working fine, now I just need to learn how to use it.
I have recorded some video footage showing how I did the upgrade and all the steps, (more so in case something went wrong and I had to refer to it, or for future reference) I do not know if I will make it public though as I don't want to annoy Siglent as they have been good to me :-)
Thank you very much to all that have been involved in producing this "upgrade path" and documenting the steps to simplify it for others such as myself, especially tv84 & Bicurico.