Based on http://stackoverflow.com/a/22857231/2509938

macroMagic.scala

import scala.annotation.StaticAnnotation
import scala.language.experimental.macros
import scala.reflect.macros.Context
import scala.reflect.ClassTag
import scala.reflect.runtime.universe.Flag._

// Add constructor arguments here.
class expand extends StaticAnnotation {
  def macroTransform(annottees: Any*) = macro Expander.expand_impl
}

object Expander {
  def f[T](v: T)(implicit ev: ClassTag[T]) = {
    ev.toString
  }

  def expand_impl(c: Context)(annottees: c.Expr[Any]*) = {
    import c.universe._

    annottees.map(_.tree) match {
      case List(q"case class $name(...$paramss)") => 
        val nameModified: TypeName = name match {
          case TypeName(s: String) => TypeName(s + "Modified")
          case _ => c.abort(c.enclosingPosition, "Not a type name")
        }
        
        val paramssModified = paramss(0) :+ ValDef(Modifiers(Flag.PARAMACCESSOR | Flag.CASEACCESSOR), 
          TermName("k"), Int.typeSymbol, EmptyTree)
        println(paramssModified)

        c.Expr[Any](
          q"""
            case class $name(...$paramss)
            class $nameModified(...$paramssModified)
          """
        )
    }
  }
}