+1 for following an established convention, if there exists one.

HOWEVER, if not, then ask yourself why do you need the buttons at all. Can this not be done directly on the grid, like MS Access used to do? I.e.:

Creation: Leave an empty line either at the beginning or at the end of the grid — or maybe a row of textboxes outside the grid. User types in there, row gets automatically created/saved.

Replace/Update: click on the cell in the grid, text gets selected automatically, typing replaces it (remember to offer an UNDO).

Delete: Either a separate button (if multiple rows may be deleted), or pop it up at the side of the row when focus is on that row. Again, offer an UNDO.