Три примера поиска и замены одного строкового выражения другим.

Первый пример показан на основе функций Split и Join. SourceString - текст для поиска, ReplaceThis - какое искать выражение в тексте, WithThis - на что менять найденное выражение

Пример 1

Function ReplaceAll(SourceString As String, ReplaceThis As String, WithThis As String)
Dim Temp As Variant
Temp = Split(SourceString, ReplaceThis)
ReplaceAll = Join(Temp, WithThis)
End Function

Private Sub Form_Load()
'этот пример меняет все найденные выражения "go" на "bad", в тексте "good boy go home"
MsgBox ReplaceAll("good boy go home", "go", "bad")
End Sub

Public Function ReplaceAll(searchstring As String, findstring As String, replacestring As String) As String
Dim curpos As Long
curpos = 1
Do
curpos = InStr(curpos, searchstring, findstring)
searchstring = Left$(searchstring, curpos - 1) & replacestring & Right$(searchstring, Len(searchstring) - curpos - Len(findstring) + 1)
Loop Until InStr(searchstring, findstring) = 0
ReplaceAll = searchstring
End Function

Private Sub Form_Load()
MsgBox ReplaceAll("good boy go home", "go", "bad")
End Sub

Private Function ReplaceSubString(str As String, ByVal substr As String, ByVal newsubstr As String)
Dim pos As Double
Dim startPos As Double
Dim new_str As String
startPos = 1
pos = InStr(str, substr)
Do While pos > 0
new_str = new_str & Mid$(str, startPos, pos - startPos) & newsubstr
startPos = pos + Len(substr)
pos = InStr(startPos, str, substr)
Loop
new_str = new_str & Mid$(str, startPos)
ReplaceSubString = new_str
End Function

Private Sub Command1_Click()
Text1.Text = ReplaceSubString(Text1.Text, " <", "<>")
End Sub

'Примеры использования
Text1.Text = ReplaceSubString(Text1.Text, ">" & vbCrLf, ">")
Text1.Text = ReplaceSubString(Text1.Text, "><", ">" & vbCrLf & "<")
Text1.Text = ReplaceSubString(Text1.Text, vbCrLf, "")
Text1.Text = ReplaceSubString(Text1.Text, "><", ">" & vbCrLf & "<")