Is it possible to change the highlighting of some specific text?

[mark-summerfield]

I am using asciidoctor-pdf with the rouge formatter.
I have defined a custom theme based on the rouge pastie theme. Here's my custom.rb file:

require 'rouge' unless defined? ::Rouge.version

module Rouge; module Themes
  class Custom < Pastie
    name 'custom'

    style Comment,         :fg => '#666666', :italic => true
    style Str,             :fg => '#808000'
    style Str::Escape,     :fg => '#808000'
    style Str::Interpol,   :fg => '#808000'
    style Str::Other,      :fg => '#808000'
    style Name::Constant,  :fg => '#000080'
    style Keyword,         :fg => '#000080', :bold => true
    style Keyword::Type,   :fg => '#80604D', :bold => true
    style Operator::Word,  :fg => '#008800', :bold => true
    style Num,             :fg => '#B400B4'
  end
end; end

I would like to make one addition. I want to color a specific word in the highlighted text ("nil"). This word is actually a Name::Constant; so I need to override that setting for this one word.
Is this possible?