What is the difference?
Where the word comes from.
Sitting auspiciously, dressed in funny clothes and a weird hat is the 皇帝， officially the boss.
皇帝， temperamental, spoilt, lascivious, hedonistic.
In China, you may have noticed, women, especially at home, loom large.
后，a person facing right, the queen on the left behind 皇帝，running the show.
To the right of 皇帝， a counterpart and reverse of 后， 司 a prince or minister, 皇帝's right-hand man, facing left towards the bossman, 皇帝。
As 皇帝 was fairly pre-occupied, what with 3000+ wives and new clothes to try on every 5 minutes, 司， always helpful, did what he could to a) sabotage the plans of 后 b) make the country run.
皇帝， 后， 司：the 3 pillars of state, hopefully making it stable!
from flag 㫃 yǎn
and phonetic snake 也 yě.
ensign wafting appearance.
Character form uses yǎn as one side
也 yě as phonetic
Qi Luan Shi character Viscount flag
thus can know shi is a flag
Maybe, just a guess, 施 acquired the meaning of 'put into practice, carry out' because, before doing anything, the Chinese like to put up many many flags and banners!
Build a new building?
Well, first we need at least 1000 flags, banners, ensigns and standards!