To do this in pure excel formula will be in my opinion unmanageably complex. The best way would be ti use a vba UDF
Function IncrCode(rng As Range) As Variant
Dim strOld As String, strNew As String
Dim i As Long
strOld = rng.Cells(1, 1).Value
strNew = ""
For i = 1 To Len(strOld)
strNew = strNew & Chr$(Asc(Mid$(strOld, i, 1)) + 1)
Next
IncrCode = strNew
End Function
Call it like this
=IncrCode(A1)
if A1
= yas111
result would be zbt222
Note that based on your question, all characters are incremented to the next ascii character, eg
9
--> :
z
--> {
Z
--> [