I remember the Old-Formats pack toolkit had an option to select sprites on a per-pack basis vs. on a per-style-used-in-level basis. I always went with the latter one, but technically, it would have been possible to have your entire pack just feature default sprites or just x-mas sprites. The latter option was probably chosen by people who made distinctive custom Holiday packs back in the day?
But of course, in Old Formats, you could basically just choose between default and x-mas anyway; the only exception I know is GigaLem's Millas, and I think he just outright replaced the default sprites with his custom ones in the context of Old-Formats Millas.
In short: I don't know if per-pack choice of a fixed sprite type is even possible anymore in New Formats, because it seems like more flexibility was what people wanted more
. What would of course work is simply setting the theme of each of those levels to "Lemminas", or whatever sprite type you want to use, no matter which graphic sets the individual levels are using. But of course, that would change the colour of Builder staircases, umbrellas, pickup skills etc. as well, rather than having those continue to go along with whatever theme would fit the graphic set of a level. And of course, it would be quite tedious to do manually for every single level.
But I guess namida can clarify this.
In the meantime, here's another popular character turned Lemming! With umbrellas, bridges, and Builder sacks made of web!
Note that there is no recolouring of Athletes compared to normal lemmings with these sprites! So this is another case of "aesthetics over strict mechanical fairness". But it simply would not look right if the lemmings sticking to a wall (=Climbers), of all skills possible, were the ones looking precisely NOT like Spider-Man!
Originally, I wanted to use the black symbiont outfit for the athletes. But that's hard to do with such low resolution, plus these sprites would only work with coloured backgrounds then.
And inverting the normal sprites to blue heads and red shirts would also be quite strange, because I'm not aware of any Spider-Man outfit (and there were many!) that looked even remotely close to such a colour scheme.