That's regime sounds like a great intent, but the simple fact is that taking a satellite launching rocket, replacing the satellite with a nuke, and aiming it back at the ground somewhere is trivial.
ICBMs use much more stable fuels so they can sit in a silo for years on end. This requires totally different engines and fuel tanks.
tldr: You can't just stick a nuke on top of a liquid fueled rocket and use it like an ICBM.
The point of MCTR is to prevent a nation from openly admitting they have such a weapon and hence it can not be used as an argument in any future negotiations.
1) Their no-first-use policy
2) Pakistan already having nuclear weapons
For example I never understood USA providing F16s to Pakistan. It is nothing but USA's attempts to escalate the tensions.
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.