Indefinite (and definite) articles are sometimes associated with a person's name. This answer by Jon Hanna is the best summary of the uses I have found. Also, another question addresses the issue that was not mentioned in the summary with the example sentence "when a defeated Napoleon rode off the battlefield and into exile", and it is followed by a couple of useful answers.
My question is related to the latter. Let me add three more examples to clarify the point.
- "muttered a startled [Michael] Fallon" (Author Alex Nunn or his Twitter)
- "an elated Sarah Storey after her victory" (Daily Telegraph)
- "one photo showing an unsmiling Francis standing next to a beaming Trump" (Washington Post
In any of these cases, as well as the Napoleon-related example, the person(s) referred to is precisely specified in the text and only one in the world.
I have heard of a hypothesis (from a friend) people sometimes use an indefinite article before a particular person's name when it is accompanied with a preceding modifier, which tends to be (though not necessarily limited?) the present or past participle form of a verb; in other words, the modifier is sandwitched between the article and person's name. All the cases listed above fit the hypothesis and the modifiers are "startled", "elated", and "unsmiling" and "beaming". If this hypothesis is correct, there is no expression like "a John Smith delighted with blah-blah" (as long as the referred John Smith is already narrowed down to a particular person in the given context).
An answer to the aforementioned question explains
It's a literary/oratorial device. You certainly wouldn't often come acrosss it in normal speech - only somewhat flamboyant prose or speechifying.
Think of it as meaning that Napoleon is a man of many aspects, victorious on other occasions, but defeated this time. Using the article implies that this is only one of several possible Napoleons that have or will exist.
The first part fits my little Googling research; it seems this use of the indefinite article is more commonly seen in novels and fictions than other types of writings.
Applying the second part to my examples, the three example sentences are interpreted as
"Fallon/Storey/Francis/Trump is a person of many aspects, but in this case s/he is only one (=startled/elated/etc) of several possible Fallon/Storey/etc",
which seems fitting.
Now I am asking for further clarifications:
- What is the condition where this use of an indefinite article is accepted? Is the above-mentioned hypothesis (i.e., always(?) having a modifier in between) correct? Are standard adjectives like "happy", as opposed to verbs in conjugation, accepted for it?
- What is the nuance of the expression? Specifically, what is the difference from the phrase without an indefinite article? For example, how about "'blah-blah', muttered startled Fallon"? I think the definite article "the" would feel a little unnatural in this case, as explained in detail in the paragraph in the previous answer.