My plans for giving TFs to Kase include him revealing that he's gender-fluid, in the sense that he doesn't really care about his gender appearance (and is fine with whichever pronouns match his appearance), but would prefer to remain male (though the latter is mainly because my plans already include a lot, and vag + preg content would add even more work). There's nothing (in-game or out) that I'm aware of to support or deny this, so unless there's something I missed it could go any way.
So, from this, I assume you mean that your plans involve Kase keeping a cock and not getting a pussy, but also being genderfluid and accepting pronouns changing? It'd be quite a bunch of work to also have a whole extra parser added just for Kase's pronouns to be added and go in and replace every spot where "he" and "his" and the like are used in his work and swap it out for the parser to choose between the male pronoun and female pronoun. Nothing against feminization, but honestly I feel like he ought to remain using male pronouns, regardless of if he's genderfluid or comfortable in being a very feminine male. Plus it'd make for a lot less work and not change that much.
Also I don't want one of the few men in this game to be turned into yet another girl with a dick. Nothing against dickgirls, I like them a lot and most of my favorite characters are women with cocks, but there's a ton of them and so few males, regardless of genital configuration, so even if he gets feminized appearance-wise and gets tits bigger than that of a serial Gush abuser's I'd still prefer for him to use male pronouns.
In fact, in my plans, that actually comes up as a plot point when discussing what mods he'll accept; he doesn't like it when people assume he's subby just because he's a kaithrit male and/or a femboy (they're right, but for the wrong reasons) and thinks that being feminised, masculinised and/or half-huskarised will stop people from making those assumptions (and it works, at least on Ramis).
I don't think I've seen anything that suggests that people just assuming he's submissive bothers him. Heck, I don't think I've seen scenes where people assume he's submissive, but I feel that if anyone were assume that, they'd do so much more for how he acts than how he would look if he were, say, standing up straight with a calm and reassured expression on his face.
Liamme is another femboy who you can meet (written by the same author as Kase, HugsAlright), and he specifically is an Ausar (another race seeming to largely be submissive, especially towards humans) and also feminine enough that Steele mistakes him for a woman, unlike Kase. However, Lia doesn't really appear overtly submissive. While he is on the bottom a decent amount of the time, whether he's laying down while sticking his dick in Steel, lying down and taking dick, or kneeling and sucking, there is not actually much in the way of submission. And it's never assumed that he's submissive by anyone, nor would I, personally, look at him and think "he's submissive."
Despite how he has the same factors as Kase in regards to being a generally "submissive" race and also being a femboy, what really makes a person's view is the attitude. Lia is confident, self-assured, stands up straight with a calm face, doesn't get nervous around others, smiles wide on first meeting, does not stutter or pause when talking outside of a few small moments where normal people would pause to think, and is rather openly flirtatious. Kase stutters, takes pauses in his speech (represented by ellipses), easily excitable and yet lost without being given direction on what he ought to do, gets nervous when someone gets close, doesn't seem to flirt at all. Honestly he's kind of just, like, anxious, but in a manner which makes him appear submissive.
So unless the mods which change him also make him more confident, less stuttery, less excitable and more stable- Essentially, unless the mods entirely eliminate who he is as a person in addition to changing his outside appearance, people would still assume he's a sub. Whether someone looks like him, or a big, hulking man with arms wider than my body, or Jessica Rabbit, they'd be more likely to be seen as and assumed to be submissive if they act the way he does than if they looked like him and moved with confidence and stability.
And given all that, I seriously doubt that people assume that he's submissive because of his race and femininity. Because if it was, then it'd be much more likely to assume Lia as submissive too, yet that isn't the case, and Kase has never mentioned anything about being seen as submissive due to appearance and race. Hell, the view of Ausar as submissive is something commonly applied by
other races onto the Ausar, but when it comes to Kaithrit, the view of Kaithrit males as being weaker and more submissive than Kaithrit female is something only done by other Kaithrit. The Codex, while talking about the history of how males were kept down and patronized and how this came to a head when they were barred from being able to get spaceship licensees because the culture viewed Kaithrit males as too "fragile" to handle piloting, it says this:
Of course, it must be noted that this patronizing attitude towards males predominantly applies to the kaithrit of Rosha; offworlders, especially those who have many generations removed from the homeworld, are far less traditional.
The anti male cat bigotry is something perpetuated primarily by the female cats on their home planet, and not by people who aren't on that home planet. Kase, having grown up on a colony with very few other Kaithrit, would have not been exposed to the sort of bigotry that assumes he's submissive for immutable factors aside from his submissiveness.
And even aside from all of that, I don't think that Kase would want to change assumptions about himself. As I said, he's comfortable with who he is, even if he's also a very anxious person, because there is no indication that he would want to change himself. He likes to be told what to do, and he likes to be pampered, and that's the sort of things that can be helped by having this outward assumption.
Tl:dr: Anyone who would assume Kase to be submissive would do so specifically because of how he acts and not because of how he looks (aside from, of course, how acting impacts appearance). The only way modwork would change an assumption of submissiveness would be to entirely erase his personality and swap it with another, and that would be effective entirely independent of his appearance, which can be shown in how Lia, who is much more feminine and also part of a race that other races are actually
shown to describe as inherently more submissive, does not ever seem to get assumed as being submissive, while having a much more confident personality than Kase. The only people who seem to automatically assume Kaithrit males are submissive are Kaithrit females who live on the Kaithrit homeworld, and as Kase grew up on a colony with only two other Kaithrit on it compared to many more people of other races, it would be unlikely to have been faced with assumptions of submission on the basis of non-personality appearance factors.