That example reminds me of a mod someone recently shared on discord where they scaled down the red dragon model to make a pseudodragon familiar. Explanation and credit by modder lostsoul:

Yes, used adult red dragon. Added Scale type 6 0.1 to roottemplate, new uuid, new character stats in character.txt

It might be something you could replicate for your examples here so you have in game scaling or even a proper scale halfling mod.

If the modder can make the dragon that small, it might be possible for halfings as well even though monsters and characters are likely to be different in many ways in the code