Probably not. The times when chemical weapons have been used since the end of WW1, both before and after their banning internationally, have been almost exclusively against opponents that lacked the capacity to retaliate in kind; it has been fear of retaliation which has prevented more widespread use, not international treaty. The British used mustard gas against rebellious tribesmen in Iraq, the Spanish used it against rebellious Arabs in Morocco, the Japanese in their invasion of China and Mussolini in his invasion of Abyssinia; on each occasion of its use, the opposing side was known to lack the capacity to retaliate.
While widespread use of chemical weapons was avoided during World War Two, all of the major powers manufactured enormous stockpiles and kept them in reserve, ready to retaliate in the event of its use by the opposition. When the Germans invaded the Soviet Union in 1941 they scrupulously avoided any use of chemical weapons (Weapons of Mass Destruction in Soviet parlance of the time, and the origin of our modern use of the term) where its use could have been detected and reported back to higher Soviet authorities; they did not hesitate to use it to eliminate pockets of Soviet resistance behind their lines, mostly in Crimea and coastal regions around the Black Sea. The Germans were well aware of the Soviet’s extensive chemical weapons program, having conducted a great deal of joint weapons development in the Soviet Union in the 1920s, when the two international pariah states cooperated extensively. The claim often made, that Hitler had an abhorrence of gas following his own gassing in WW1 is false; Hitler was never gassed – his medical records show this conclusively, noting that he was only ever hospitalised for hysterical blindness – and on more than one occasion expressed the belief to German journalists that gas was a humane form or warfare that would lead to fewer casualties (presumably he only meant German casualties), besides which, Wehrmacht use of gas in the Black Sea region shows that there was no wholesale prohibition on its use.
Every soldier landing on the beaches of Normandy carried a gas mask (the bulky cases the masks were carried in can often be seen in the old film footage) and large numbers of gas artillery shells were available for immediate retaliatory use. The British and Americans were not manufacturing nerve gas (something the Germans mistakenly believed they were), but had enormous quantities of mustard gas available.
Since the end of World War Two, chemical weapons have again been used on a number of occasions, and again almost always against opponents who lacked the capacity to retaliate; the Egyptians used nerve gas extensively during the Yemen Civil War in 1963, the Cubans used it in Angola and Saddam used it in the Iran-Iraq War; in all but the last case the opposition did not have the capacity to manufacture chemical weapons.
It is notable that while Iran did not have chemical weapons when Saddam first used them early in the war, and so could not have immediately retaliated, they did have the industrial capacity to manufacture them and could have retaliated in kind to later attacks – they simply chose not to. The most peculiar thing about this is that they did not manufacture gas in the hope of deterring Saddam. It is possible that, knowing that Saddam would not been deterred and realising that after they acquired chemical weapons the demand for their use would have been overwhelming, the Iranian leadership made the moral decision to prevent their own use of chemical weapons the only way they could – by never acquiring them in the first place.
Something also worth noting: while quite a number of nations have been able to manufacture nerve gas, the number of countries that have been able to develop the chemicals necessary to stabilise the nerve gas for long-term storage has been much fewer; without these stabilising chemicals nerve gases have limited shelf-lives and become less lethal over time, generally after more than a year in storage. This means that stocks of nerve weapons need to be constantly rebuilt – an expensive and costly process, not to mention dangerous in the extreme.