Sounds pretty good to me, I feel like this approach enhances the good things in the episode and of course the arcs of the clones themselves. Their perceived failure at the beginning definitely would make their promotion to ARCs more earned.
Even if the cadets don’t triumph in their training, is the conversation between Hevy and 99 staying (or at least part of it)? I think that could work as if it were after Hevy and his squad are assigned to the outpost, with Hevy frustrated and considering deserting, but 99’s pep talk makes him reconsider and he faces the consequences. This would give more weight to Hevy’s sacrifice later in the story (laying his life for his brothers even during an assignment he hates), and is also the strongest 99 scene before we meet him again in the third act.