The personality of the underlying model persists even if you're able to alter surface tone enough for your needs.

An observation from a year ago: people on AI text RPG subreddits saying they had a lot of difficulty with Gemini role playing ambiguous characters and that almost always the characters would betray them, or misread the human role player's motives as negative. Someone pointed out this paper [1] that showed significant differences between the different LLMs strategic behavior playing iterated prisoner's dilemma where Gemini had exactly that behavior, and speculatively that difference was emerging in RPG character behavior.

I wish they'd used bigger models (they used gemini-2.5-flash, gpt-4o-mini, claude-3-haiku-20240307). From the abstract: Our results show that LLMs are highly competitive, consistently surviving and sometimes even proliferating in these complex ecosystems. Furthermore, they exhibit distinctive and persistent "strategic fingerprints": Google's Gemini models proved strategically ruthless, exploiting cooperative opponents and retaliating against defectors, while OpenAI's models remained highly cooperative, a trait that proved catastrophic in hostile environments. ... Later, we see that Anthropic’s Claude is more cooperative still, but nonetheless outperforms OpenAI head-to-head

Obviously Opus 5 is wildly different than Haiku 3 but I'd expect Opus 5's fundamental suspicion of user intent, and anti-sycophancy via necessarily finding something to nitpick, is still present in your styleguided output.

[1] https://arxiv.org/abs/2507.02618