You have should do the same for the blocks. if its already in the drawing either redefine, reinsert, or alert you that its already in the drawing.
(if (tblsearch "block" "block2") ;checks for block2
(vl-cmdf "_.Insert" "block2=*c:\\Myblock\\symbols\\block2.dwg" pause "" "") ;(vl-cmdf "_.Insert" "*block2" pause "" "") or (Alert "\nBlock2 is already defined in drawing")
(vl-cmdf "_.Insert" "*c:\\Myblock\\symbols\\block2.dwg" pause "" "")
(setvar 'clayer "0")
)