In several sources ther eis mention of animals of a certain disposituion (chioleric, plegmatic....) being summoned/cursed/whatever using the elements.
The bodily humors are also related to the elements.
The question then is: can you modify/create emotions modifying the bodily humors of a target? Cause someone to fall in love, for example, or provoque a visceral hate for someone. Is this explained in Art & Acadme? In the Jerbiton chapter of Societates?
Am I coming up with a non sequitur here? After writing it it seems so....
Emotions can indeed be affected by using magic "(Medicinal) Controlling" from Hedge Magic - Revised. I believe permits the character to manipulate people in such as fashion. As to whether this is possible with Hermetic Magic is another question. If so I would probably use a Rego Corpus spell with an elemental requisite and use the Mentem guidelines. Lots of Finesse rolls would be required as well!
There is a difference between emotion and complexion. Your natural humoural balance is called your complexion, and it gives you your overall temperament and personality - your 'factory settings', so to speak. These drift with time; adolescents tend to be more choleric, adults are more melancholic, and seniors are more phlegmatic. Currently there is no Hermetic magic which affects complexion, although A&A suggests that a minor breakthrough in Corpus would allow it.
Emotion is a different beast altogether. There are five basic emotions - timor (fear/worry), ira (hatred/anger), tristitia (sorrow/gloom), laetitia (delight/love), and gaudium (bliss/joy). These are provoked by factors external to the body through the estimation, one of the inner wits. Emotions are therefore part of Mentem, and can be invoked directly with CrMe spells. There is some interplay -- a choleric person is more prone to ira because of his naturally hot complexion, and more resistant to timor, which is a cold emotion (laetitia and tristitia are moist and dry, respectively; gaudium is perfectly balanced and the only emotion that cannot be taken in excess).
Elemental Magic (from HMRE) should evoke emotions by emulating Mentem, rather than messing with the humours. However, since the five basic emotions are tied to the elements, this is a legitimate use of the power. It is up to the SG as to whether other magic can influence emotions. Strictly speaking, you can't manipulate a humour to provoke an emotion. Humours are affected by emotions, not the other way around. However, a humoural change could make someone more prone to an emotion by altering their complexion; for example, impose a temporary Personality Trait of Fearful, meaning that anything frightening provokes a roll to avoid the screaming abjabs.
Summary: Any spell or power that emulates Mentem can affect emotions. Spells or powers that can affect Corpus may be able to influence baseline personality.
With respect to medicinal theriacs; it should certainly be possible to alter one's humoural balance with pharmaceuticals. Of course, this is natural rather than supernatural magic. I would treat Weak Potency as a +1 to a Personality Trait, and every magnitude of Potency adds a further +1. The base level of the theriac would depend on the amount of time you want the drug to last.