The provision that Iran's acquirement of heavy weapons be regulated by the UNSC is not legally binding, i.e. it is not subject to enforcement under Chapter 7. But even if it were, a permanent member like Russia could always get away with violating a UNSC resolution, as any fallout from attempting to enforce the provisions could be dealt with by Russian vetoes.
If Russia were to proceed with such actions that the US would strongly object to, then US-Russian relations could worsen. A lot depends here on what the US and Russia have discussed privately at the time the text of the provisions was drafted. E.g. did Russia get guarantees from the US that any proposed Russian weapons sales would be evaluated objectively based on Iran's needs to modernize its army and not face blanked bans? Did the US change its mind after the Iranian missile tests? So, these are all relevant factors that we can only guess about.
It is quite analogous to UNSC resolution 1441 which was adopted after the US gave guarantees that the enforcement provisions in it would not be used to start a war against Iraq. A second UNSC resolution would be needed. But later the US and Britain changed their mind on that, in their opinion the relevant circumstances had changed. Whatever disagreements there were, there was of course nothing the other UNSC members could do to stop the US and Britain.