I wrote a blog post on the Solomani.
Here's a thought for you.
The Solomani Party and their overtly racist policies amount to essentially a "political fad" for a time that waxes and wanes periodically, rather than being some kind of all powerful unifying
TRVTH that unites and overcomes everything in the path of the Solomani peoples forever. In other words, it's a "tribal instinct" that sort of comes and goes throughout history.
Now consider the possibility of portraying that overtly racist policy in a different light.
Rather than being the all powerful defining force of the Solomani identity ... what if instead it was more of a "brittle grip" kind of situation?
The overtly racist policies of the Solomani Party are somehow "failing" to retain the "hearts and minds" of the Solomani people, meaning that the influence of the Party is waning rather than growing. How would the Party react to such a slow rejection and turning away from their desired racial purity goals? Easy answer ... by doubling down on the things that are losing them support, becoming more extreme and more intolerant, to the detriment of all in order to prop up the few who remain aligned with their beliefs and views and still support the Party.
In other words, the Solomani Party still has a "grip" on the Solomani Confederation ... but that influence is waning ... and the Solomani Party doesn't like this turn of events one bit. So they tighten their "grip" on the Solomani, but the means they use to do so are "brittle" and if they squeeze too hard the Solomani Party will be replaced as a major power broker in the Confederation, relegated to the backwater worlds that still support their policies (despite the damage it does to their societies and development) and becoming an even more extremist movement in the process.
So if you're creating material in which the Solomani Party has entered this "downward slide" while trying to maintain their "brittle grip" on the Solomani Rim you can have all kinds of settings and adventures in which the Solomani Party is a factor in society without necessarily being a beneficial or automatically respected factor (and possibly a hindrance to local parochial interests). That then sets up a scenario in which "the center cannot hold" and fragmentation becomes the overarching trajectory of the narrative, in which new forces and interests arise to fill the vacuum left behind by the retreating influence of the Solomani Party and their overtly racist politics, schemes and actions.
In other words, a slow crumbling slide of support ... rather than a sudden shattering (like what happened to end the multiple Imperiums). That way, you aren't just telling the same stories with a different cast of characters.
The Solomani Party was a "solution to a problem" for the Solomani in the past and one that they accepted (readily) in that past.
But times have changed ... and in the "present" the Solomani party is more of a "problem seeking a solution" than they have been which will refuse to go quietly into the dustbin of history recounting the days of Humaniti among the stars.
Princess Leia: "The more you tighten your grip Tarkin, the more star systems will slip through your fingers."
Such is the destiny of almost all extremist movements as they "purify" themselves through increasing extremism into an evolutionary dead end that cannot survive their own fanaticism. They may hold sway for a time, but rarely are they stable enough to endure for all eternity ... particularly when confronted with freedom of thought and the continuing imperative of enlightened self-interest.
So ... if you characterize the Solomani Party as having a "brittle grip" on Solomani society, which is in decline (and the Party doesn't want to be in decline, because being in decline isn't "for the good of the party" per Orwell's 1984) ... the setting of the Solomani Rim gets a LOT more interesting and diverse!
Your mileage may vary, of course.