Which Glider physics change do you mean? This change happened many versions ago. Before that physics change, it was possible to assign a Shimmier to a Glider standing in front of a Stacker’s stack and have that lemming land on top of the stack. This is a trick I used in a couple of levels from Lemmings Open Air, but I’ve swapped that out ages ago.
I think the reason the Glider physics were changed originally was that they opened their parachute at a different point in time than Floaters did? Or some discrepancy between regular Fallers and Gliders? namida might remember the details better.
Perhaps you’ve simply missed that update when it happened?
Or is there yet another new Glider physics change (from 2022) I don’t know about yet?

It’s hard for me to know which version of the editor you mean by “old NeoLemmix editor”. Are you still talking about an older New-Formats version (12.X)?
Obviously, the Old-Formats editor (10.13) still had old Glider physics. But it also didn’t have any Shimmiers yet.
That’s why people advocate against using the Old-Formats editor, at least if you plan to make your pack available for New Formats, too.
This is different from when I started working on Lemmings World Tour, which was during the transition phase to New Formats.
(I originally wanted to wait with that until New Formats was available, because I already wanted Lemmings World Tour to include Jumpers. But if I had waited that long until the Jumper was introduced to finish the pack, it still wouldn’t be completed today.)
EDIT: Alright, judging from your other posts in other threads, you were talking about an older version of New-Formats NeoLemmix; one that already included the Shimmier, but neither the Slider or Laserer, nor the Jumper, which was introduced much earlier (and already
after that Glider physics change).