Horary Astrology.

So from what I've read before, when it comes to horary astrology, 7 planets are involved which if those planets team up with one of the 12 sun signs it has a message, a meaning. Those 7 planets are, Venus, Mars, Mercury, Jupiter, Sun, Moon, Saturn. What would happen if Pluto, Neptune, and Uranus showed up in with one of the 12 signs? Say, Neptune in Capricorn, Pluto in Gemini, or Uranus in Virgo? Is there such thing?

Yes Horary does usually keep to the seven traditional planets, though there are readers who try to incorporate the outer three. The main reason why horary readers keep to the traditional 7 is that the texts explaining the process were all written before the discovery of the outers, so it's by no means clear how they can be involved. Most modern texts on horary are attempts to expain the traditional process but in modern English and with modern examples.

Horary depends heavily on rulership of signs and through the signs, houses. The outers do not fit in to the system of rulership (which is not related to affinity but is related to position relative to Sun and Moon). I've seen some readers who use the outers in the same way that fixed stars are used, that is close aspects are considered but otherwise they are ignored. You will find one or two readers who will try to use modern rulerships (a hotchpotch of traditional reasons and affinities).

Also many modern practitioners of Astrology are suspicious of horary. It does not fit with their perception of the modern psychological nature of Astrology. Therefore, few modern practioners attempt to adapt horary to the modern view and those that do practice, such as Tony Louis, use traditional methods for their horary work (see Anthony Luis, Horary Astrology, Plain and Simple).

When I cast a horary chart I have set the software to exclude the outers - they simply don't show up in the chart, so they are not considered at all. Indeed I don't have them showing up as the default for any Astrology I do but then that's a matter of personal choice and practice.