A Nashorn (JavaScript) script to search out variable definitions in comments and use their values in other places in the file where placeholder comments are present.

variabilize.jjs

//	This is a Nashorn (JavaScript) script to search out variable definitions in comments and use their values
//	in other places in the file where placeholder comments are present.
//
//	SYNOPSIS
//	
//		jjs variablize.jjs -- ${PATH}
//
//	DESCRIPTION	
//	
//		Go through file at ${PATH} and search out all variable definitions as per regular expression:
//		
//			\/\*\s*(\w*)\s*=\s*(.*?)\s*\*\/
//			
//		The pattern matches stings such as:
//		
//			/* foo = bar */
//			
//		Where group 1 (foo) is the variable name, group 2 (bar) is the value.
//		
//		
//		With these definitions, search the rest of ${PATH} for regular expression:
//		
//			\/\*\s*(\w*)\s*\*\/(.*?)\/\*\*\/
//			
//		The pattern matches strings such as:
//		
//			/* foo */ .. /**/
//			
//		Where group 1 (foo) is the variable name, group 2 ( .. ) will be replaced by the value (bar)
//

// args
var filePath = arguments[0];

// imports
var String=Java.type("java.lang.String");
var StringBuffer=Java.type("java.lang.StringBuffer");
var File=Java.type("java.io.File");
var FileSystems=Java.type("java.nio.file.FileSystems");
var Files=Java.type("java.nio.file.Files");
var FileWriter=Java.type("java.io.FileWriter");
var StandardCharsets=Java.type("java.nio.charset.StandardCharsets");

var buf = new String(Files.readAllBytes(FileSystems.getDefault().getPath(filePath)), StandardCharsets.UTF_8);

var matches = {}
var definitionRegexp = /\/\*\s*(\w*)\s*=\s*(.*?)\s*\*\//g;
var match = definitionRegexp.exec(buf);
while (match != null) {
	matches[match[1]] = match[2];
	print("DEF " + match[1] + " = " + match[2])
	match = definitionRegexp.exec(buf);
}

for (var match in matches) {
	var replacementRegexp = new RegExp('(\\/\\*\\s*'+match+'\\s*\\*\\/)(.*?)\\/\\*\\*\\/','g');
	buf = buf.replace(replacementRegexp,'$1' + matches[match] + '/**/');
}

var fw = new FileWriter(FileSystems.getDefault().getPath(filePath));
fw.write(buf);
fw.close();

Adding as "External Tool" in IntelliJ

Go to "External Tools"

For Program point to Nashorn: C:\Program Files\Java\jdk1.8.0_171\bin\jjs.exe
For Arguments point to your script on file system: C:\Users\jner\usr\variabilize.jjs -- "$FilePath$"
For Working directory point to some temp (it's not used): C:\Users\jner\tmp