# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/^#([A-Z]):\s/$1:] /gm;t' <<< "Ludus øfficiis suåvitate sea in, ius utinam vivendum no, mei nostrud necessitatibus te?
#A: This is some info.
#B: Some more info.
#C: More stuff.
#A: The end.
Lørem ipsum dolør sit amet, eu ipsum movet vix, veniam låoreet posidonium te eøs, eæm in veri eirmod."
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html