回答ｺﾒﾝﾄにしたがって修正しました｡
お試しください｡

A列しかないという条件で作りました｡
空白以外に置換したい文字があれば､mainの
Call delHoge("C:/test/", "csv", "#")
の3番目の引数で指定してください｡2種類以上の文字を書くこともできます｡

Option Explicit

'1列処理
Function convCol(sour As String, str As String) As String
 Dim dest As String
 Dim re As Object
 Dim remat As Variant
 Dim pat As String
 dest = sour
 
  '指定文字削除
 If (str <> "") Then
 Set re = CreateObject("VBScript.RegExp")
 pat = "[" & str & "]+"
 With re
 .Pattern = pat
 .IgnoreCase = True
 .Global = True
 End With
 dest = re.Replace(dest, "")
 Set re = Nothing
 End If

  '@のあとに数字がある場合は行削除
 Set re = CreateObject("VBScript.RegExp")
 pat = "@[0-90123456789]+"
 With re
 .Pattern = pat
 .IgnoreCase = True
 .Global = True
 Set remat = .Execute(dest)
 If remat.Count > 0 Then dest = ""
 End With
 Set re = Nothing
 
 convCol = dest
End Function


'1行処理
Function convRow(buf As String, ln As Long, path As String, fname As String, str As String) As String
 Dim items As String, dest As String
 Dim ch As String
 
' items = Split(buf, ",") '列に分解
 buf = Trim(buf)  '先頭･末尾の空白削除
  'ｸｫｰﾃｰｼｮﾝ削除
 ch = Left(buf, 1)
 If (ch = "'" Or ch = """") Then buf = Mid(buf, 2, Len(buf) - 2)
  '1列変換
 dest = convCol(buf, str)
 convRow = dest
End Function

'1ﾌｧｲﾙ処理
Sub convFile(path As String, fname As String, str As String)
 Dim ln As Long
 Dim buf As String
 Dim fname1 As String, fname2 As String
 fname1 = path & fname
 fname2 = path & fname & ".$$$"
 Open fname1 For Input As #1
 Open fname2 For Output As #2
 ln = 1
 Do Until EOF(1)
 Line Input #1, buf
 buf = convRow(buf, ln, path, fname, str)
 If (buf <> "") Then Print #2, buf
 ln = ln + 1
 Loop
 Close #1
 Close #2
 Kill fname1  'ｵﾘｼﾞﾅﾙ･ﾌｧｲﾙ削除
 Name fname2 As fname1
End Sub

'ﾌｧｲﾙ探索＋処理実行
Sub delHoge(path As String, ext As String, str As String)
 Dim fcol As Object, re As Object
 Dim flist As Variant, remat As Variant
 Dim pat As String
  'ｻﾌﾞﾃﾞｨﾚｸﾄﾘ探索
 Set fcol = CreateObject("Scripting.FileSystemObject").GetFolder(path).SubFolders
 For Each flist In fcol
 Call delHoge(path & flist.Name & "/", ext, str)
 Next flist
 Set fcol = Nothing
  '処理対象ﾌｧｲﾙ探索＋処理実行
 Set fcol = CreateObject("Scripting.FileSystemObject").GetFolder(path).Files
 Set re = CreateObject("VBScript.RegExp")
 pat = "\." & ext & "$"
 With re
 .Pattern = pat
 .IgnoreCase = True
 .Global = True
 For Each flist In fcol
 Set remat = .Execute(flist.Name)
 If remat.Count > 0 Then Call convFile(path, flist.Name, str)
 Next flist
 End With
 Set re = Nothing
 Set fcol = Nothing
End Sub

Sub main()
 Call delHoge("C:/test/", "csv", "#")
End Sub