REPLACEB( Text ; Position ; Length ; NewText )
Text: A text expression or reference to a cell containing a text expression in which the characters are to be replaced.
Position: the character position from which text is to be replaced.
Length: the number of characters to be replaced.
NewText: the text to be inserted.
=REPLACEB("ᄩᄔᄕᄜᄝᄞᄠᄢᄣᄫᄬᄭᄮᄯᄲᄶ";4;1;"ab") returns "ᄩ abᄕᄜᄝᄞᄠᄢᄣᄫᄬᄭᄮᄯᄲᄶ" .