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Not in the easy way, not with MRI

    $ irb
    2.4.1 :001 > 1.class
     => Integer 
    2.4.1 :002 > class Integer
    2.4.1 :003?>   def 1
    2.4.1 :004?>     2
    2.4.1 :005?>     end
    2.4.1 :006?>   end
    SyntaxError: (irb):3: syntax error, unexpected tINTEGER
    def 1
         ^
    (irb):6: syntax error, unexpected keyword_end, expecting end-of-input

That's not unexpected as small numeric literals are magic in Ruby, for performance reasons.

More evidence:

    2.4.1 :001 > class Integer
    2.4.1 :002?>   define_method(:one) { 1 }
    2.4.1 :003?>   end
     => :one 
    2.4.1 :004 > Integer.one
    NoMethodError: undefined method `one' for Integer:Class
    2.4.1 :005 > Integer.new.one
    NoMethodError: undefined method `new' for Integer:Class
    2.4.1 :006 > Integer.new
    NoMethodError: undefined method `new' for Integer:Class
    2.4.1 :007 > class Klass
    2.4.1 :008?>   define_method(:one) { 1 }
    2.4.1 :009?>   end
     => :one
    2.4.1 :010 > Klass.one
    NoMethodError: undefined method `one' for XY:Class
    2.4.1 :011 > Klass.new.one
     => 1

So Integer is not like other classes and the actual reason for that http://archive.oreilly.com/pub/post/the_ruby_value_1.html

TLDR MRI gets the value of the number directly from value of the C pointer and saves the lookup. It's a 1 in the lowest bit and the integer value in the others. That's why 0.object_id == 1, 1.object_id == 3, etc

Obviously that's implementation dependent but I guess no Ruby implementation is going us to redefine integers if MRI does not.