Still many bytes, but I really like your approach of taking the postmatch to indend the substitution! =)

like this it's quick and easy to get the triangular part of the tree!!! 

  DB<<70>> $_=$"x15;s: :$'#$`$`#\n:g;print
              ##
             #  #
            #    #
           #      #
          #        #
         #          #
        #            #
       #              #
      #                #
     #                  #
    #                    #
   #                      #
  #                        #
 #                          #
#                            #


  DB<<71>> $_=$"x15;s: :$_=$`;y/ /#/;"$'$_$_\n":ge;print

             ##
            ####
           ######
          ########
         ##########
        ############
       ##############
      ################
     ##################
    ####################
   ######################
  ########################
 ##########################
############################

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In reply to Re^3: Resetting pos() within a RegEx? by LanX
in thread Resetting pos() within a RegEx? by LanX

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