substitute multiple line pattern in sed

Today I faced a problem with a multiline replacement. I did not want to write a sophisticated regex.
I just wanted to get a copy-pasted block of code and put it in place of the old one. Selected weapon - sed.
I've chosen the /begin/,/end/ matching syntax.

['test' input file]

111
222
333
  if (aaa) {
     bbbbb
  }xxx
  }
444
  while (0) {
     ccccc
  }
666

['change' script]

#!/usr/bin/ksh

sed '
/if (aaa)/,/\   }$/ c\
  CHANGE\
     WAS\
  MADE
' \
test

[session]

$ ./change
111
222
333
  CHANGE
     WAS
  MADE
444
  while (0) {
     ccccc
  }
666