As for trope changes- I would say the biggest change in the past 10 years is that following the success of PMMM a lot more magical girl shows are adult-focused and darker than the standard fare. It's not as common now but for a long time we were inundated with Madoka clones, lol. Except most of them didn't have PMMM's heart and soul so they kinda fall flat.
I'll push back on this one slightly - PMMM accelerated the trend and got quite a few projects greenlit (including some that desperately wanted to be another PMMM - looking at you, Selector WIXOSS!) but the shift towards adult-focused magical girls predates PMMM by a few years. There were experiments in that direction as early as the 1990s (Galaxy Fraulein Yuna comes to mind, arguably Utena as well depending on whether you consider it part of the genre - also there's the likes of Princess Tutu though that's early 2000s, and while Full Moon wo Sagashite is very shoujo it's a very dark shoujo) and they really kick in with Fall 2004 which brought us Nanoha (which the PMMM staff was absolutely without a shadow of a doubt familiar with, Shinbou directed Nanoha S1) and Mai-HiME (whose status as part of the genre was debated due to shedding many of the genre trappings and adding mons - IIRC there's an interview where the PMMM staff noted that they made sure to hew to the genre trappings and I doubt that's unrelated - but I strongly suspect the PMMM staff was familiar with it; it's the prototype for a couple of PMMM features (I'd put good odds Kyubey was directly inspired by Nagi from Mai-HiME) and I suspect Kajiura's HiME OST is what got her hired for PMMM in the first place (Magia and Mysterioso even follow the same naming scheme as Kajiura's main battle themes for the Mai franchise, namely Mezame and MATERIALISE)).
Also in 2011 we got Symphogear (which used a blatant mix of Nanoha and Mai-HiME inspiration, it just uses a different HiME arc than PMMM does), and while I suspect Symphogear had enough time to make some changes to account for PMMM it was 100% greenlit before PMMM aired.
In general I've also noticed a steady decline of the genre. The 90s and 2000s were full of traditional magical girl warrior shows, and in the wake of PMMM the 2010s had a lot of "edgy" magical girl shows. But now, aside from Precure, there really don't seem to be consistent entries in the genre.
It makes me very sad. It's not like magical girls are extinct or anything, far from it, but imo it's not the popular genre it used to be. I swear 75% of the anime coming out nowadays is isekai or vaguely fantasy themed in general and it just holds no appeal to me. You'd think with the dozens upon dozens of anime that get made every year they could squeeze in more magical girl shows than Precure.
Sadly, nothing new about this either - I've noted this before elsewhere but magical girls now are in almost exactly the same place that mecha was circa 2005, where everything is either a reboot/continuation of an existing franchise, an attempt to imitate the show that went nova, or in a different subgenre (and the one surviving non-magical girl warrior subgenre is dying as well, since the more idol-themed magical girl shows - and increasingly Precure as well, for that matter - have been getting outcompeted by the modern shoujo-targeted pure idol shows). Same root causes, too: one franchise cornered the toy market making kids' shows outside of that franchise uneconomical (Gundam and Precure, respectively), then a show came along and went nova that is simultaneously a deconstruction and an example of the genre done so well as to be its apotheosis overshadowing even very well done predecessors (Eva/Madoka).
If magical girls follow mecha's path then we'll see Mahou Shoujo Gurren Lagann in a couple of years (possibly by Shaft or a Shaft vet) followed by a string of attempts to reboot the genre that all mostly fail with a big surge in them starting around 2035 or so. (Then again, there may not quite be a niche for Mahou Shoujo Gurren Lagann. Eva did a good job tearing apart mecha to its foundations but while it manages to put its characters back together it left the genre in pieces; PMMM 12 instead neatly wraps up mahou shoujo in a nice bow.)