I think so too. Unless that country is the USA or powerful European one. Attacking supply routes is possible but here we're talking about small arms and maybe manpads and atgms. That's possible to smuggle without being obvious and too easily attacked by Russian military. It would be declaration of war on neigbors who provide supply line but if they can prove it, it's possible this may happen.
This along with Sweden and Finland joining NATO could incite whole European theater war.
Oh yes, if Romania or Poland or Slovakia, the border states, are caught supplying weapons to future insurgents in Russian controlled territory, they re getting bombed.
And this will result in retaliation by NATO. It will not end well for anyone.