Of course it would be possible to use the 3D models done for 1/12 for smaller scales, HOWEVER, you have to realize that at 1/24 the parts are half the size (genius maths, eh?) and that means if we have designed parts at the limits of the printers resolution for 1/12 scale, they will not work at 1/24 scale. Say doing a radiator mesh / grille in 1/12 scale would be showing finer detail than in 1/24 scale. If you would scale it down from 1/12 to 1/24, the thickness and width of the mesh elements might be below the threshold of the printer, i.e. too thin, hence not printable. So that might be an issue and it may lead to having to do parts differently for the various scales. Sticking with the example of radiators. Take the 330 P4 radiator at the front. You could do that using photoetch spacers of various diameters, small followed by large by small by large (you get the picture - also see the P4 done by Marcus here, with PE from Rasputen). The entire assembly threaded onto a 3D printed rod with additional U-shaped connectors. Scaling that down to half would either have you use PE with half the thickness (could be difficult to get consistent good etching results) to have the exact same look as 1/12 (which would be using the same 3D models) or redoing it in such a way that formerly 4 spacers (large, small, large, small) are reduced to 2 spacers (large, small).
Another thing to keep in mind is surface detail, say ribs on a gearbox or the cooling fins on an aircooled cylinder (think Porsche engine). What could be scale correct thickness in 1/12 might be too thin to reproduce in 1/24. This needs to be considered in advance while doing the models. If I were to do something like that, I would create a separate layer (or object) with the fins scale correct in 1/12 and again for 1/24 where the thickness would not be scale correct but printable - if you get what I'm trying to say. Basically keep the model "modular" to allow for different scales.
And as the topic of scales has been brought up - I think the first step would be to poll what model should be the initial project (say Monaco 312 T4), what scale(s) (if more than one) it should be and see who or how many folks around here would be interested to guesstimate the "scope" of this project and then take it from there.
Feel free to call out "Bingo" if I have ticked too many BS bingo boxes with that "essay" above
