/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
        final String string = "Select a, CASE \n"
		+ "WHEN 1 \n"
		+ "THEN \n"
		+ "   CASE some text\n"
		+ "     WHEN 2 THEN A \n"
		+ "   END \n"
		+ "END";
		String regex = "(?i)(\\bcase\\s+)\\S((?!\\bCASE\\s).)*?(?=\\s+when)";
        String repl = string.replaceAll(regex, "$1var");
        System.out.println(repl);
	}
}

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