'Launch signal' isn't the issue, you'd need to work past the PAL used for the weapon to be any significant threat, and soviet PALs were relatively complex based

'Launch signal' isn't the issue, you'd need to work past the PAL used for the weapon to be any significant threat, and soviet PALs were relatively complex based on multiple path lengths and timing deviations. You could just rip the PAL out and build a new detonation timing system, but then you'd be re-doing a large part of the trial-and-error phase of the manhatten project. It's not something that could happen in hours or weeks. Realistically more like months or years.