Det er meget uklart for mig hvad du leder efter.
Henvisningen til ASP og beskrivelsen matcher ikke i min optik.
Men her er "noget":
Imports System
Imports System.Collections.Generic
Imports System.Text.RegularExpressions
Namespace E
Public Class Program
Public Shared Function Replace(input As String, replacements As Dictionary(Of String, String)) As String
Dim res As String = input
Dim re As New Regex("{(\w+)}")
For Each m As Match In re.Matches(input)
Dim id As String = m.Groups(1).Value
res = res.Replace("{" & id & "}", If(replacements.ContainsKey(id), replacements(id), ""))
Next
Return res
End Function
Public Shared Sub Main(args As String())
Dim input As String = "A: {A} B: {B} C: {C} D: {D}"
Dim replacements As New Dictionary(Of String, String)()
replacements.Add("A", "This is A")
replacements.Add("C", "This is C")
Dim output As String = Replace(input, replacements)
Console.WriteLine(input)
Console.WriteLine(output)
Console.ReadKey()
End Sub
End Class
End Namespace