R.Muralikrishnan, MPI for Empirical Aesthetics. This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Licence.
#!/usr/bin/awk
#####################################
# Awk script to replace a certian field on rows that occur between a START and STOP pattern.
# These lines are printed with necessary changes, other lines are printed as is.
#
# Execute as: awk -f Replace-using-start-stop-pattern.awk Input.txt > Ouput.txt
#             Use the accompanying wrapper shell script for multiple files
#
# Author: R. Muralikrishnan
#####################################

# General Logic: Use text fields/patterns in the file that indicate a starting and ending point 
#                between which changes need to be made. 
#                For lines within these limits, change necessary fields as required, but don't print them yet.
#                In a second step without any conditional statement, print all lines 
#                (...which will include the changes we made in the previous step).


BEGIN{FS="= "; i = 1;}  # Input field separator is '= ';

# Use the start-stop pattern recognition to treat lines occurring between the patterns.

(substr($2,2,3)=="syl"),(substr($2,2,3)=="MAU"){  # The brace has to be here...since we've used the () form 
                                                  # of the 'if' check.  Taking it to the next line won't work...
                                                  # in effect acting as though the check were not at all there.
  
  # We are on lines that have name = "syl" and name = "MAU"
  
  
  # Now, if the first field is "text" and 
  # the second one (with FS="= ") begins with a double-quote, 
  # but it is not empty (i.e., not ""), then
  # change the second field to "C1", "C2", "C3" or "C4" (with the double-quotes)
  if ($1~/text/ && $2~/\"/ && $2!~/\"\"/)
  {
    $2="= \"C"i"\"";   # What we want is, in effect   = "C1"   etc.
    #print $0;         # Don't print the line yet...it will be taken care of in the general section below.
    i++;
  }
}
{print $0}