I think there is a clearly stated break, which is this:
‘in the new period … the old formula … becomes incorrect and must inevitably be replaced by another formula, one that affirms the possibility of the victory of socialism in one country.’ 'The Social-Democratic Deviation in our party', Report delivered at the Fifteenth all-union conference of the CPSU(B), Nov 1, 1926 in Stalin On the Opposition (Foreign Language Press, Peking 1974)
Stalin was aware that his was a new policy. The policy was an attempt to deal with the stabilisation of capitalism post-world war I, under the Dawes plan. The policy was pragmatic - an attempt to retrench - an not wrong for that. It was though, delusional, in that there was no possibility of building socialism in Russia, without access to western technology, on terms that simply were not on offer.
The negative consequences of the 'socialism in one country' policy were that European communist parties were tempted to mix up diplomatic advantage for the USSR with what was best for building revolution in their own countries. At key moments, the advice from Moscow was to put off the revolution, where it jeopardised the Soviet Union's own diplomacy. At that point, you could say that 'Stalinism' was a reactionary influence. In the USSR the police measures that the bureaucracy took to shore up the bad policy were extreme, and destructive.