Boru,
St. Thomas does not say that a non-olive oil is allowed to completely REPLACE olive oil. He says that another non-olive oil is allowed to SUPPLEMENT olive oil in the mixture, if and only if the supplies of olive oil are running low.
In a mixture of oils, olive oil is still present to some degree. And it is spread throughout that mixture. So the "matter" of the Sacrament is present in all of the mixed oil to some degree. No one said that the oil applied for the Sacrament had to be PURE olive oil all by itself. In fact, Chrism is a mixture of balsam and olive oil. Therefore, it is clearly not a problem if other non-oily substances are included in the mixture. So why would it be a problem to supplement a little non-olive oil in the case of necessity? It is not a problem, according to the Church and St. Thomas. The essential thing is that there must be enough olive oil in the mixture so that when the mixture is applied, there is olive oil included in that application.
As I said, in his Reply to Objection 4, St. Thomas says that the concern that olive oil might not be available in some locale is of no importance. He says that because the Sacrament of Confirmation is not a necessary Sacrament, the recipients can wait for the next shipment of olive oil rather than use a non-olive oil as a wholesale REPLACEMENT for olive oil. In other words, it would be worse to use no olive oil than to delay the reception of the Sacrament. This is because to use no olive oil in the Chrism would make it invalid matter.
Anyway, why are you arguing about this? What is your angle here? Are you just trying to be argumentative? FWIW, Abp. Lefebvre, who you seem to respect, agreed that olive oil must be used in the Chrism for the Sacrament to be valid.
I'm trying to get you to step outside your box and see things how the Church sees things. You are attacking a Vicar of Christ over this. Yes, the prescribed and preferred oil is Olive oil. No question. But there has been a precedent for similar oils being used in the history of the Church, when there is a case of necessity. The very fact that the Church allowed this - and allowed the mixing of oils - and allowed the mixing of balsam - when St. James prescribed only olive oil, proves that when it comes to the Matter used in Sacraments that have been determined by the Church, and by the power of the Church, the Church can make modifications as St. Pius XII outlines. That is the core point. Pope Paul VI, gave bishops special permission to bless similar oil in cases/places where it is very difficult to acquire olive oil, rather than let a Catholic die without Extreme Unction. As Pope, who Christ said can 'bind and loosen', he has the power and authority to do so. And I stress again, Christ instituted the Matter and Form for Baptism and the Holy Eucharist
and then handed over His teaching authority to His Church. This is a scriptural fact. From that point on it was the Church who decided, guided by the Holy Ghost.
Writes Fr. John Bligh in his 1956 theological book 'Ordination to the Priesthood':
"The official adoption of the terminology of 'matter' and 'form' had the unfortunate effect of encouraging theologians to think that the essential rites of every sacrament must be unchangeable. In the physical world whenever there is a distinction of matter and of substantial form, there are distinct bodies...that form plus that matter makes that body. Hence the terminology of matter and form, borrowed ...from the physical world (erroneously suggests) that a change of the matter and form of the sacraments would mean..new sacraments..other than those instituted by Christ...". Hence it was concluded that the Church has no power to altar the matter and form of any of the sacraments. This erroneously conclusion...".