After an initial test, I've decided to swap out Cancel Replay in favour of Select Walking Lemming, since Replay mode can be cancelled simply by clicking anywhere in the empty screen, and this tends to be how I cancel Replay mode when playing using a Mouse and Keyboard anyway. Meanwhile, the ability to select a Walker from behind another active Lemming seems like it'll be very useful for finer control.
I've considered adding in the Highlight Lemming function, but I tend to find this very fiddly to use even with a Keyboard and Mouse, so I'm unlikely to reach for it all that much. If I find that any of the other buttons I've assigned are mostly redundant, though, I will reconsider putting this one into the setup; maybe the function will make more sense to me on a Gamepad...
Pause and Fast Forward are both very useful in the Trigger position, so I'm leaving these as they are (I originally had these assigned to Start and Select, but found that I used them a lot so it makes sense to have them in a more readily accessible area of the pad).
The large Skip Forward and Skip Backward buttons didn't get used much, but I was testing using the first few levels of L1 which don't require much skipping. Fast Forward was more than sufficient to get through the slower parts of the levels, and since I've played these levels a million times I never needed to do large Backward skips.
I can imagine that the skip buttons will get used way more when playing levels I'm less familiar with.
Overall thoughts so far:
NeoLemmix is great when played using a Gamepad! It adds another layer of tangibility which, whilst slowing down the gameplay somewhat, helps to bring back some of that feeling of "herding kittens" which permeated original Lemmings. I didn't use the finer game controls during the initial test, so I'll have to play a more complex level which requires more detailed and precise inputs to get a sense of how it handles for more intricate gameplay.
More on this later!