You may be allowed to sell butter as margarine since the the composition of the lipids for margarine allows also bovine lipids in general and butter fat in particular (and some margarines partially consist of butter fat).
But it doesn't make sense economically: margarines are butter substitutes prepared from cheaper lipids (mostly(?) vegetable oils that are hardened: saturated, but also e.g. tallow).
When you clarify butter, you keep the lipid fracton, the butter fat. For margarines in the usual sense of the word, the lipid fraction of the margarine will not be the same as butter fat.
I see from the comments that you are actually wondering whether the clarification process can be reversed.
- The traditional clarification by heating is probably difficult, since the proteins undergo heat denaturation, and that is irreversible.
- However, industrially, butter fat is apparently prepared by a cold process, and that may be more suitable. The product also has less fat (>96 % compared to 99.5 % with the heating process), while of the remainder only up to 0.2 % - so the remainder are probably mostly leftover proteins. (source, sorry, in German)
German language Wikipedia says about clarified butter (Butterschmalz)
Die europäische Butter wird zur Entwässerung – das entwässerte reine Fett ist das Butterschmalz – nur bis etwa 90 °C erhitzt und kann im Bedarfsfall durch Zugabe von Wasser wieder teilweise in Butter rückverwandelt werden. (Die Proteine bleiben denaturiert.) Ghee wird bei Temperaturen über 100 °C entwässert und ist gar nicht mehr in Butter rückführbar.
translation (deepl translator with small corrections):
For dehydration - the dehydrated pure fat is the clarified butter - European butter is only heated up to about 90 °C and can be partially reconverted into butter by adding water if necessary. (The proteins remain denatured.) Ghee is dehydrated at temperatures above 100 °C and can no longer be re-converted into butter.
Side note: in German, "Butterschmalz" (the clarified butter obtained by keeping the butter molten for a time, maybe half an hour: the protein denatures and one fraction sinks to the bottom, another fraction yields a "foam" and the water evaporates) is subtly different from "geklärte Butter" (literally clarified butter, prepared by melting and immediately taking off the foam and decanting from the whey fraction below the molten butter).
Apparently, there was a time when emulsifying clarified butter would have made sense:
German language Wikipedia on Butterschmalz:
Die Herstellung von Butterschmalz wurde eine Zeit lang von der EU subventioniert, um den (damaligen) Butterüberschuss („Butterberg“) abzubauen. Um eine Rückführung in Butter durch Emulgierung zu verhindern, was einem Subventionsbetrug gleichkäme, musste (gesetzlich vorgeschrieben) Stigmasterin dem Butterschmalz zugefügt werden, das dann als Indikator diente. Da der „Butterberg“ seit 2008 kein Problem mehr ist, endete die Subventionierung und mit ihr auch die Pflicht zur Beigabe von Stigmasterin.
translation, again deepl + a bit of help:
For a while, the EU subsidised the production of clarified butter in order to reduce the (then) butter surplus ("butter mountain"). In order to prevent a return to butter by emulsification, which would have been tantamount to subsidy fraud, stigmasterol (required by law) had to be added to the clarified butter, which served as an indicator. Since the "butter mountain" is no longer a problem since 2008, the subsidy and with it the obligation to add stigmasterol ended.
(Stigmasterol is a substance naturally occuring in plants and also in [some] vegetable oils, but not in butter)