This depends on your definition of informal terms like "letter", "character" etc.
The typographic term for combinations like this is "digraph". (Wikipedia's definition: "A digraph [...] is a pair of characters used in the orthography of a language to write either a single phoneme [...] or a sequence of phonemes that does not correspond to the normal values of the two characters combined".)
Whether digraphs have separate keys on a keyboard, are treated as distinct for the purposes of alphabetisation, whether speakers of the language think of them as separate "letters" when spelling out a word and so on, are all separate issues and varies between languages (or, more precisely, between the conventions for writing a certain language).
Agree this is the part of the Freedom of Information Request that is relevant to this, and that this is a sensible translation.
My interpretation of this is that Irmeli Krans is asking Mats Gehlin how to formally log additional information (in the form of some kind of verbal communication with the prosecutor) and ensure that this information is associated with the case file.
The back and forth, again as far as I understand the implicit context and the terminology used, concerns how to do this technically. Gehlin suggests it be logged as a separate, additional interview. Krans is worried that will look weird, since there was only one actual interview undertaken by Krans. Krans then suggests that the technically correct way of doing this would be to change the original interview and sign that.
I read "change" here as implying "append the new information in that document". There is no obvious suggestion of editing the existing text of the original interview.
The typographic term for combinations like this is "digraph". (Wikipedia's definition: "A digraph [...] is a pair of characters used in the orthography of a language to write either a single phoneme [...] or a sequence of phonemes that does not correspond to the normal values of the two characters combined".)
Whether digraphs have separate keys on a keyboard, are treated as distinct for the purposes of alphabetisation, whether speakers of the language think of them as separate "letters" when spelling out a word and so on, are all separate issues and varies between languages (or, more precisely, between the conventions for writing a certain language).