No, you probably shouldn't replace the writer's "who" with "whom".
Well, you physically can do that, but you probably shouldn't. For if you did, then the result would be considered by many (especially those who are teachers) to be ungrammatical.
The result would be considered to be ungrammatical (by them) because the relativized element or gap in the relative clause is functioning as a subject of an embedded content clause, and so, the relative pronoun is supposedly required (by Dialect A speakers) to be in nominative case: "who".
- In response to the inquiry of a man(i) [ who(i) she may not have realized [ __(i) was a reporter] ], . . .
Notice that the gap in the embedded content clause is functioning as the subject: "he was a reporter." And so, the expected relative pronoun is the nominative "who".
ASIDE: But be aware that there is a dialect within today's standard English whose speakers will usually use the accusative "whom" in these types of situations. CGEL labels that dialect as Dialect B in their discussion of it on pages 466-7, subsection "(e) Subject of an embedded content clause". CGEL considers this type of usage (Dialect B) to be "grammatical in some dialect(s) only", which they mark as "%". One such example of Dialect B usage is: % those whom he thought were guilty -- page 466, [37.a]. CGEL says, on page 467:
Dialect A, which selects nominative, has more speakers and is the one recommended by the manuals, but here is no reason to say that it is inherently better or more grammatically correct than Dialect B, which selects accusative: the dialects just have different rules.
NOTE: CGEL is the 2002 reference grammar by Huddleston and Pullum et al., The Cambridge Grammar of the English Language (CGEL).