REPLACEB
Returns text where an old text is replaced with a new text, using byte positions.
REPLACEB( Text ; Position ; Length ; NewText )
Text: A text expression or reference to a cell containing a text expression in which the bytes are to be replaced.
Position: the byte position from which text is to be replaced.
Length: the number of bytes to be replaced.
NewText: the text to be inserted.
=REPLACEB("ᄩᄔᄕᄜᄝᄞᄠᄢᄣᄫᄬá„ᄮᄯᄲᄶ";4;1;"ab") returns "á„© abᄕᄜᄝᄞᄠᄢᄣᄫᄬá„ᄮᄯᄲᄶ" .