Rails - Mar 2011 - (2.3.5) removing validations

(sorry for misposting this to rubyonrails-core earlier)

Today I tried to remove (actually overwrite) a validation from a model,
from within a plugin.

This was the original validation:
  validates_length_of :login, :maximum => 30

This was the only code I could come up with to replace it:

  def self.included(base)
    base.class_eval do
      @validate_callbacks.delete_if { |callback|
        begin
          (callback.method.respond_to?(:binding)) &&
            (eval("attrs", callback.method.binding).first == :login)
&&
            (callback.options[:maximum] == 30)
        rescue NameError
          false
        end
      }

    validates_length_of(:login, :maximum => 75)
  end

Now in this case I could also have changed the options[:maximum] on the
callback, but either way - is there a cleaner way?

  -- niklas