broadly, it means interchangeable; but it's another of those law terms which isn't very fungible in ordinary speech.

1832 Austin Jurispr. (1879) II. xlvi. 807 When a thing which is the subject of an obligation+must be delivered in specie, the thing is not fungible, i.e. that very thing, and not another thing of the same or another class in lieu of it must be delivered. Where the subject of the obligation is a thing of a given class, the thing is said to be fungible, i.e. the delivery of any object which answers to the generic description will satisfy the terms of the obligation. 1886 Sat. Rev. 25 Dec. 853 A certain number of persons+do not+regard books as ‘fungible’, but exercise a choice as to the books they read.


I guess you could stretch the point and say that specific loyalties are interchangeable with other loyalties, but yes, why not just say 'changeable'? (or check out Roget if you must: inconstant, fickle, hebdomadal, flaskisable(!), commutable, mutal, protean, shifty, transitive, variable, unstable...)