I'll stress again, the US did it with no instruction book. Most of those great scientists were theoretical physiscists. There is nothing theoretical that needs doing. Many were involved in crunching numbers. Computers do that now. The US did get to test, and tested exactly once. Testing of components prior to that is not something that would be particularly detectable. The challenges today are just about the precision engineering and manufacturing.

I get that you think that countries routinely neglect maintenance of their nuclear arsenals just because using them is not necessary to MAD. It's not that complicated, it's just wrong. The US and Russia used to do regular inspections of each-others weapons to maintain MAD. That wasn't all that long ago. There is no telling when such an agreement might come into play again which would greatly disadvantage countries not keeping things up. We also know for certain, because of those inspections, that the US and Russia had established proper maintenance routines. There is reason to believe that Russia may not have kept it all up, but it's really doubtful that the US abandoned that maintenance.

If a non-nuclear power like Iran were to suddenly declare that they are now a nuclear power, some amount of proof would be required before it was taken seriously. To think otherwise isn't ignorant, it's insane. I have to wonder why you think they haven't tried your clever hack already.