The ascendant sign is the cusp of the first house, the sign that was rising in the East at the time of birth, and will give an indication of the way you are perceived by others. It is a learnt way of being, though you will probably never remember actually learning it. It is a type of behavior that you adopt as a child because, at that time, you found it to be most appropriate. It is developed mainly to impress our parents. We may well be behaving in a certain manner that is frowned upon by our parents and so we adopt a behavior pattern that seems to produce better results.
By adulthood it is well established and feels very natural, many have called it our mask, this is because it can hide what is actually behind it, but it is not real, not the real you, people who get close to you may be able to see behind the mask. Sometimes, the mask becomes too real and you start to believe it yourself and assume that that is the way you are rather than the way you act. Sometimes this can cause problems with self-expression and a feeling of not being able to be true to one's self. This adopted behavior may not be the most appropriate behavior to be displaying at this moment in time but we may somehow feel locked into it.
The Ascendant then is more of a habit than a true globule of energy as represented by the planets. As you are no doubt aware habits can be hard to break and if you are thinking of breaking it you may well find it easier to modify it or find ways that allow more of the real you to shine through. Having said that it should not be impossible to change ascendants. Of course we are getting into arguments about fate and freewill which often crop up. You were born at a certain time and at that time your ascendant sign was rising above the eastern horizon, so how can you change that.
Well, when no time is known we can use Solar houses, where the Sun sign is considered to be your ascendant and we work from there. There is I think a lot to be said for this method because it shows what would happen were you to be totally true to your inner self, the Sun. It makes one think does it not that in like manner you could possibly put any planet you like on the ascendant and work perhaps with Jupiterian energy or Mercurial energy. To put signs on the Ascendant that are not inhabited by planets may be more of a problem but nevertheless not impossible. We have more than the first house remember and should you say, wish to have Sagittarius on your Ascendant, had no planets there but Jupiter in Aries. You perhaps could, by expressing your Jupiter in a fifth house manner, build up a Sagittarian Ascendant.
This of course would not be easy, calling for some very sustained effort and mostly some would say why bother, you are what you are, make the best of it and it is true, personal growth need not be so drastic but I do think the possibility is there. We can be almost anything we want to be. The irony of it is, if things are going well, you are already what you want to be and no sign is any worse or better than any other, but it is good to know we have a choice.
The main point though is to keep the correct view of what the Ascendant actually means. The Ascendant is a very prominent and sensitive point in the chart but it is not by any stretch of the imagination a Planet. Its usefulness lies in the view of the Ascendant as a starting point. It must be remembered here that what is being discussed is natal not prenatal astrology. From an astrological view point the Ascendant is a starting point that leads on to the second, third and fourth houses and ends in the twelfth.
Qabalisticly the Ascendant can be seen as a starting point that runs horizontally across the chart and ends in the Descendent, balancing and drawing in the MC and IC on the way, leading from awareness of self to the ultimate surrender of self in union with the Divine. This journey from the Ascendant to the Descendant represents the Central Pillar on the Tree of Life. To look at the Ascendant in this way does make it correspond to Malkuth, as we have seen the Ascendant is a way of acting, Malkuth is much more than that. The Ascendant can be placed in Malkuth but it is not Malkuth. In fact it is probably better to think of it as it is, one part of a great circle.