The Child Fix broke Child Height Slider Mods and Modders cannot fix it

I tried to report this as a bug report, but it was immediately closed as "mod related" despite being the EA side's fault, so here we are.

I have no idea what the root cause is because we modders don't have access to whatever code y'all fixed it in, but I can't seem to apply any modded facial attributes to Child sims after the Toddler/Infants/Child body and face distortions | EA Forums - 11928891 fix - when I try to set them, nothing seems to happen and they're not set when I poll the facial attributes again.

My best guess is that y'all might be copying a proto over but only the modifiers that you recognize, effectively clearing all modded modifiers?

The code I'm using:

facial_attributes = PersistenceBlobs_pb2.BlobSimFacialCustomizationData()
facial_attributes.MergeFromString(sim_info.facial_attributes)
modified_facial_attributes = PersistenceBlobs_pb2.BlobSimFacialCustomizationData()

# copy all modifiers that are not from my mod from fa over to mfa
for ml in ['face', 'aged_face', 'aged_body', 'body']:
    src = getattr(facial_attributes, ml + '_modifiers')
    dst = getattr(modified_facial_attributes, ml + '_modifiers')
    for modifier in src:
        if modifier.key not in MY_MODIFIERS:
            dst.append(modifier)
for sculpt in facial_attributes.sculpts:
    modified_facial_attributes.sculpts.append(sculpt)

# same results if aged_body_modifiers instead, or both
modified_facial_attributes.body_modifiers.append(modifier)
sim_info.facial_attributes = modified_facial_attributes.SerializeToString()
# same results with or without this
sim_info.resend_facial_attributes()

If I instead try to apply my custom modifiers using CAS hotspots in CAS, then the sim changes visually inside CAS, but the changes do not survive the Accept button to leave CAS.

I have user reports suggesting that this does not occur in offline mode, for whatever reason. In any event, this breaks all Height Slider mods for Child sims.

Platform: PC, Windows 10, EA app

Bonus questions for things I've never been clear about:
1. What exactly do the new aged_body_modifiers and aged_face_modifiers do and when?
2. What exactly do the .resend_[property] methods even do?

EA_Cadeplz help