As stated in my OP:
From what I can see, it looks as if I may just be able to change the domain (SETTING) used for this in the .OVPN file whilst leaving all else the same - but I remain uncertain & do not wish to break it by skipping any needed steps.
(I have a vague memory of possibly also regenerating some files for this, but after ~3 years the memory is just too vague...)
I am asking about reconfiguring OpenVPN !!
Yes, it will be for a different domain to be used, but that is very easy...
The source being used for the DDNS could be anything, really - I need to keep this connection from failing is all.
Thanks.
P.S.:
I first set up OpenVPN for this distant connection ~5 years ago.
This will be the 3rd time I will be forced to change the DDNS domain in OpenVPN due to outside forces beyond my control.
So - this time I aim to do something a bit more permanent !!