Public Function fnFormat( _
  ByVal rng As Range) As String
    fnFormat = Format(rng.Value, "@@@ @@@ @@@")
End Function

A1 = "123abc456"
B1 = "=fnFormat(A1)"

Public Function fnFormat2( _
  ByVal rng As Range) As String
    Dim intI As Integer
    Dim blnFlag As Boolean
    Dim strValue As String
    Dim strTemp As String
    Dim strSymb As String *  1 
    
    strValue = rng.Value
    
    For intI =  1  To Len(strValue)
        strSymb = Mid(strValue, intI,  1 )
        
        If intI =  1  Then
            blnFlag = IsNumeric(strSymb)
            strTemp = strTemp & strSymb
        Else
            If CInt(blnFlag) <> Not CInt(IsNumeric(strSymb)) Then
                strTemp = strTemp & strSymb
            Else
                strTemp = strTemp & Chr( 32 ) & strSymb
                blnFlag = Not blnFlag
            End If
        End If
    Next intI
    
    fnFormat2 = strTemp
End Function

A1 = "123abc456"
B1 = "=fnFormat2(A1)"