Hello.
I had the
same situation, as destination yard for ballast trains had no the half of actually-existing branches to grinding facilities, being simplified in current route's version.
So, I couldn't haul empty dumpcars and hopper-dozers out from visible place by shunter, terminate them there and after time - spawn loaded train there (or trigger a new consist's variant with all cars loaded), to haul it back to yard, where icould be picked up by mainline locomotive and depart backward.
https://www.elvastower.com/forums/uploads/monthly_03_2022/post-11269-0-86172200-1648493618_thumb.jpg
So, I didn't make static consists, but instead - made new trains with termination on siding, they have been on, after several time period. Correspondingly - I have to spawn loaded variants on siding, then - hold them there for some time, before mainline locomotive come to pick them up, forming outbound train.
I didn't have courage to re-build that station to give it missing pull-out spurs, real switch-streets and industrial branches - in addition, all signaling would be spoiled around. Where a shunter stands - at the far-left - there actually is a huge grinding-sorting factory with some branches, loading doszens of cars daily.