This question is my extension to this one. Please excuse if it sounds too naive, as I am not a physicist by trade.
From the above linked question and answers to it I understand no physical phenomena or properties in classical mechanics or thermodynamics can be "truly" negative, but only relative to some arbitrary reference point. I'm unsure about electrostatics, though. Electric charge occurs naturally in two elementary forms of a same "size", but opposite "sign". This "sign" is more than just a mathematical fiction; it is physically observable, as attraction resp. repulsion of other charges, depending on their sign. The question for me is whether opposite charges make these entities completely different by nature, or are they simply properties of one and the same entity.
For example, can we say that positron and electron are physically the same object, once carrying a "positive" and once a "negative" charge, or are they different kinds of objects that happen to have a same mass? Something along the lines: "If we flip the spin of an electron, it still remains an electron, but with an opposite spin". Can we make this analogy regarding electron/positron: If we flip the charge of a negatively charged "x-tron" (an electron), it still remains an "x-tron", but with a positive charge?
From my limited knowledge of quantum mechanics, I recon the answer to this last question is "No", implying that even in electrostatics negative numbers are just a mathematical trick we use to simplify descriptions of the nature, but I'd appreciate if someone could confirm that.
I acknowledge that my above reasoning is related to this question, but it is not the same IMO.