claudio
antonio
claudio
michele

claudia
antonio
claudio
michele

sed -e '1,/claudio/s/claudio/claudia/' nomi

sed -e '0,/claudio/ s/claudio/claudia/' nomi

awk

$ awk 'NR==1,/claudio/{sub(/claudio/, "claudia")} 1' nomi
claudia
antonio
claudio
michele

sed -n ':a;N;$bb;ba;:b;s/(claudi)o/1a/;p' file
sed -n '1h;1!H;${g;s/(claudi)o/1a/;p;}' file

sed -n '                # don't implicitly print input
  :a                    # label "a"
  N                     # append next line to pattern space
  $bb                   # at the last line, goto "b"
  ba                    # goto "a"
  :b                    # label "b"
  s/(claudi)o/1a/    # replace
  p                     # and print
' file

sed -n '                # don't implicitly print input
  1h                    # put line 1 in the hold space
  1!H                   # for subsequent lines, append to hold space
  ${                    # on the last line
    g                     # put the hold space in pattern space
    s/(claudi)o/1a/    # replace
    p                     # print
  }
' file

$ awk '!f && /claudio/ {$0="claudia"; f=1}1' file
claudia
antonio
claudio
michele

sed '$H;x;1,/claudio/s/claudio/claudia/;1d' <<IN
claudio
antonio
claudio
michele
IN

claudia
antonio
claudio
michele

sed --in-place=*.bak -e "1 h;1! H;$! d;$ {g;s/claudio/claudia/;}" -- nomi

export chngFrom=claudio
export chngTo=claudia
sed --in-place=*.bak -e "1 h;1! H;$! d;$ {g;s/${chngFrom}/${chngTo}/;}" -- nomi

sed -n '/claudio/{s/o/a/;bx};p;b;:x;p;n;bx' nomi

sed -n '      # do not print lines by default
  /claudio/ { # on lines that match "claudio" do ...
    s/o/a/    # replace "o" with "a"
    bx        # goto label x
  }           # end of do block
  p           # print the pattern space
  b           # go to the end of the script, continue with next line
  :x          # the label x for goto commands
  p           # print the pattern space
  n           # load the next line in the pattern space (clearing old contents)
  bx          # goto the label x
  ' nomi

sed -n '/claudia/{p;Q}'

sed -n '           # don't print input
    /claudia/      # regex search
    {              # when match is found do
    p;             # print line
    Q              # quit sed, don't print last buffered line
    {              # end do block

sed '/(claudi)o/!b;//s//1a/;:1;n;b1'

sed '
/(claudi)o/!b    # Match the regex `claudio`. But in two parts `claudi` and `o`
                   # and, for lines that do not match yet go to end (print).
//s//1a/          # For one line that match the previous regex, change o to a.
:1                 # label to loop from now on.
n                  # read next line (it gets auto printed).
b1                 # keep (only) printing to the end of file.
'

echo 'claudio
antonio
claudio
michele' | sed -z 's/claudio/claudia/'

claudia
antonio
claudio
michele