# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(?=:90C:|:90D:)(.*?)ABC(\S+)/$1XYZ$2/gm;t' <<< " :20: LAIDKZPABCL90165LZJABC
:90: LZ,90509LAOABCXL,XKPA;AOLZ
:90C: KDOLASABC9080690ABD
:90D: ABDBABC906AODIPALKD
:90L: AND9011112XXXADABC
:90: AKLZPDOAMXNA,;POAS"
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