Finally caught an episode when it aired! Have a thoughts-dump that took way too long to write out.
First off, the post-transformation Changeling hive looks great. And the new Changelings are cute too (I know they've been in other episodes, but this is the first time they've gotten any sort of focus, and they're adorable).
I liked Pharynx's design at the start of the episode. Maybe it's because he's got red on him. Although his post-transformation look was nice too. Probably because it kept the red-and-black color scheme he had before and just brightened it up a bit (to more of a red-and-dark-blue). And made him almost as tall as Thorax.
And then he started attacking plants and I just found him oddly comical. I dunno why exactly.
Overall, I ended up liking Pharynx. The fact that he kinda had a point about the new Changelings being soft to the point that it was starting to be a problem (as shown by their failure to handle the giant mole beyond just leading it away from the hive and hoping it stays away) didn't hurt him, and my general enjoyment of his screen time was pretty much necessary if I was going to like To Change A Changeling. So, glad that worked out.
And Thorax wasn't a complete pushover (or at the very least, he can now get annoyed with Starlight and Trixie when the former leads the aforementioned giant mole straight to his hive... dunno about the rest of the hive tho, he still seems fairly passive with them... although, Pharynx is the only Changeling we've seen that hasn't transformed in this episode, so either all the non-new-Changelings left or Thorax managed to assertiveness them into accepting the new way of life off-screen). At least it seems like he's retaining his lesson from Triple Threat. Even if he's still working on it tho, it's good to see him again.
Also, glad they had a line saying that Starlight and Trixie were just going for a surprise visit to Thorax and the Changelings. It kinda explains why Spike isn't with them, and the Spikelessness was something that kinda bugged me going into this episode.
Speaking of Starlight and Trixie, their not really being able to solve this problem was... not something I expected, but it was good, I think. They largely made things worse, though that's mostly because Pharynx was eavesdropping on them when they wrote him off as unfixable (and Starlight leading the giant mole straight to the Changeling hive was... not that great of an idea, though I can kinda see the logic behind her plan). They said the right things when they were talking to Thorax about his brother problem (even if that's mostly down to not telling Thorax to expel his brother from the hive like they were saying they would earlier), and Starlight's speech worked out pretty well in the end (even if the initial reaction to it was most likely "Well then we CHOOSE to not help Pharynx!").
Also, it was nice to see Starlight worsen a problem without using magic. Has that happened before now?
The resolution coming down to Thorax and Pharynx talking out their problems (after making a mole beat itself into submission) was a good thing, I feel. Better than Starlight/Trixie/Thorax doing a speech that solves the problem like I expected (in hindsight, I would've been okay with Thorax speeching his brother into transforming, but I prefer the way the episode went, with the two of them having a brief feelings forum about it).
If I had any real problem with this episode, it'd be that Trixie kinda felt unnecessary. She wasn't really detrimental, I just kept wondering what she was doing there.
So, overall, I enjoyed this. Pharynx is good, Thorax is good, the new Changelings are good, and Starlight and Trixie are bad at solving Changeling problems. And that's also good.