And in any case it's was not simply removing the safety devices on the weapons, you need to be able to target the ICBMs at Russia, which Ukraine could not do:
> In fact, the presence of strategic nuclear missiles on its territory posed several dilemmas to a Ukraine hypothetically bent on keeping them to deter Russia. The SS-24s do not have the ability to strike targets at relatively short distances (that is, below about 2000 km); the variable-range SS- 19s are able, but Ukraine cannot properly maintain them. [...] the SS-19s were built in Russia and use a highly toxic and volatile liquid fuel. To complicate matters further, targeting programs and blocking devices for the SS-24 are Russian made. The retargeting of ICBM is probably impossible without geodetic data from satellites which are not available to Kiev.
> Cruise missiles for strategic bombers stored in Ukraine have long been 'disabled in place'.[...] As with ICBMs, however, retargeting them would be impossible for Ukraine, which does not have access to data from geodetic satellites; the same goes for computer maintenance.
From SIPRI research report 10; The Soviet Nuclear Weapon Legacy
So Ukraine did not have usable weapons at hand. But it did, and does, certainly have the capacity to build entirely new weapons, if given time.
