I don't think this is Rider cosplaying Tatsuta, but Tatsuta with radically longer hair and glasses. The admiral addresses her as Tatsuta, and only exclaims Rider to acknowledge the resemblance. There's a mention of Akashi, I think in the context of "Akashi's shady new drugupgrade" to explain the sudden hair growth. Also, their relative heights in the third and fourth panels are consistent with how Mimofu has drawn his admiral and Tatsuta in the past, while Rider is significantly taller.
Thanks to [Akashi's restorative drug], even my eyesight has gotten worse.
Things Involving Shipgirls That Are No Longer Allowed, Rule 2020: It has come to our attention that some of you girls might need glasses. Those who don't already use glasses are required to report to medical for an eye evaluation.
Alanis, killed by a drug interaction
Tatsuta-san, what's with the hair!?You're Rider!!Thanks to that, even my eyesight has gotten worse. So, she said she'll return it to what it once was.Oh....Oh? You're staring that much.Admiral likes this sort of thing?Your pubic hair has gotten longer....It's sticking out.Akashi-chan said that it's a side effect of her restorative drug.