Trying to change Case of particular character in a cell - vba

Question

I am trying to change a case of particular character in a cell but i think i am missing very small thing in it.
Eg.
The cell has value 'A for Apple and GORILLA wears pajama'
so i am trying to change case of individual 'A' into lower case 'a'.
Now there are 3 scenarios:
A can be in Starting of cell.
A can be in Middle of cell.
A can be in End of cell.
for the middle one I have solution:
Activecell.value = Replace(Activecell.value," A "," a ",vbTextCompare)
but for other 2 when I'm trying to do change other A's also changing, for example:
Activecell.value = Replace(Activecell.value,"A ","a ",vbTextCompare)
this is giving answer 'a for Apple and GORILLa wears pajama'
wherein I'm trying to get 'a for Apple and GORILLA wears pajama'
my code is
Do Until ActiveCell.Offset(0, -cnt).Value = "" And ActiveCell.Offset(0, -cnt1).Value = ""
actc = ActiveCell.Value
If actc = "" Then
ActiveCell.Offset(1, 0).Select
Else
ActiveCell.Value = Replace(ActiveCell.Value, " m ", " m ", , , vbTextCompare)
ActiveCell.Value = Replace(ActiveCell.Value, " cm ", " cm ", , , vbTextCompare)
ActiveCell.Value = Replace(ActiveCell.Value, " dm ", " dm ", , , vbTextCompare)
ActiveCell.Value = Replace(ActiveCell.Value, " mm ", " mm ", , , vbTextCompare)
ActiveCell.Value = Replace(ActiveCell.Value, " mg ", " mg ", , , vbTextCompare)
End If
Loop

Answer 1

To replace only the "A " in the beginning check this in particular.
If Left$(ActiveCell.Value, 2) = "A " Then
ActiveCell.Value = "a" & Right$(ActiveCell.Value, Len(ActiveCell.Value) - 1))
End If
Accordingly for the " A" in the end (Even if I don't know about sentences ending with " A")
If Right$(ActiveCell.Value, 2) = " A" Then
ActiveCell.Value = Left$(ActiveCell.Value, Len(ActiveCell.Value) - 1)) & "a"
End If

Answer 2

The VBA Replace function will replace ALL instances of the substring in the target string.
To specify beginning and/or end of the string, you can test for the presence of the substring and, if it is present, use a different function (I chose to use the Replace Worksheet function) to replace only that character. Examine the following code snippet for an example.
With ActiveCell
If .Value Like "A*" Then .Value = WorksheetFunction.Replace(.Value, 1, 1, "a") 'Beginning only
If .Value Like "*A" Then .Value = WorksheetFunction.Replace(.Value, Len(.Value), 1, "a") 'End only
End With
If, on the other hand, you want the sentence to start (or end) with the word A, implying there is a space after (or before) the A, then change the Like pattern to reflect that "A *" or `* A"
If all of those substrings are, in fact, words, and you want to replace them all in each ActiveCell, you can either construct multiple loops along the format of what you are doing, or you could use Regular Expressions.
For example, the following will replace all instances of the capitals you have indicated with their lower case equivalents, whether they are at the beginning, middle or end.
The macro first matches all of the instances of the different words in sPat, and then cycles through the sentence to replace them. (Note that we must go from last to first in the loop, since the lengths of each word may not be the same).
Option Explicit
Sub doit()
ActiveCell = replaceCaps(ActiveCell)
End Sub
Function replaceCaps(ByRef S As String)
Const sPat As String = "\b(?:A|M|CM|DM|MM|MG)\b"
Dim RE As Object, MC As Object
Dim I As Long
Set RE = CreateObject("vbscript.regexp")
With RE
.Global = True
.ignorecase = False
.Pattern = sPat
If .test(S) = True Then
Set MC = .Execute(S)
For I = MC.Count - 1 To 0 Step -1
S = WorksheetFunction.Replace(S, MC(I).firstindex + 1, Len(MC(I)), LCase(MC(I)))
Next I
replaceCaps = S
Else
replaceCaps = S
End If
End With
End Function