You are mixing perspectives.

Trivial for a nation-state is different than trivial for a person. A nation like India could accidentally lose the amount of money required to hire a team of 20 to do the engineering to mount a working nuke to a working rocket.

Intentionally paying and assembling that same team would be trivial for a nation like India, USA, China or Russia. It could be as simple as a single line item on some military spending bill.

I think he meant that relative to the difficulty of actually creating a platform for accurate delivery of payloads to space, changing out the payload is, in fact, trivial

Thanks, I'm well aware of what he meant. Rockets have very specific requirements in terms of payload weight and shape. So do nukes. Matching the two would take actual engineering effort. Enough that I may not be possible to do so in total secrecy. Which is what this thread was originally talking about.