It is possible, here's the brief tutorial, you have to interact with the political factions that spawn like 10~ years into the game, spending influence to supress or promote factions, many of them being defined by an ethic(you will probably have a xenophobe and militarist faction), to make your pops switch to the ethics you want(though this happens over a period of time), once a certain ethic has 20% of political power support(derived from pops, generally a slave/worker pop being worth less politically than a leader pop) you have the option to spend 500 influence to 'embrace' a faction shifting you towards that factions ethic.



For example lets say I am a egalitarian, spiritualist, pacifist, and I want to become xenophobe, then I find the xenophobe faction and promote them(hovering over the little xenophobe symbol on the top will tell you how much political power that faction will gain until the faction political power stabilizes), but in order to become xenophobe I must lose one of the ethics I currently possess, the game will get rid of the ethic with the least political support in your empire (with an exeption for when you swap to an ethic that is directly opposite of one you currently have, a xenophobe, fanatic militarist can't become a xenophobe, xenophile, militarist), lets say that was spiritualist, so once I reach 20% support for xenophobe I can spend 500 influence to embrace the faction, I will then become, egalitarian, xenophobe, pacifist.



So simply put to get from Authoritarian/Fanatic Militarists to Xenophobe/Fanatic Militarists you just have to promote the xenophobe faction, supress the authoritarian faction to make sure they are the ethic you lose, then embrace the xenophobe faction once you have 20% support for it.

I am sure there are guides online for this but there you go