@BCMan - now that's helpful, thank you.
There's so much assumed knowledge in this broader community - case in point, I did not know that the shipping options can change the order in which they display, hence invalidating index. I always assumed the order was determined by something server-side, and static. I get that the developers here will know this, but for people like myself (and let's be honest, a substantial part of BCs marketing is aimed at people like me, with some *modest* coding skills but not at professional level), this sort of stuff is like mana.
Would I be correct in thinking that I need to add a hash check to the url to prevent updating?
And I will say once more, I do not want anyone to write code for me That's not how you learn, or at least, not how I learn.
Cheers, and will post back with success or a gif of a PC sailing through a window...