VBA macro which writes a new macro from string on the fly - string

Question

Is it possible to create Excel VBA macro from a string variable?
Suppose we have FirstMacro:
Sub FirstMacro()
Dim MyString
MyString = "Sub SecondMacro()" & Chr(13) & Chr(10) & "MsgBox " & Chr(34) & "Hello" & Chr(34) & Chr(13) & Chr(10) & "End Sub"
Debug.Print MyString
'Here be code that magicly creates SecondMacro
End Sub
Running the macro, I want to create SecondMacro which is stored in VBA string variable. The second macro can be created either below in the same module or in a new module.
So the second macro from string looks like this:
Sub SecondMacro()
MsgBox "Hello"
End Sub

Answer 1

Sure is possible. It should be noted that you can't add/delete from the module you're running code in.
This will append the code at the end of the module. If you can avoid this though you should, I only use it for adding code to buttons that I've added programatically.
With Workbooks(ThisWorkbook.Name).VBProject.VBComponents("MyModuleHere").CodeModule
.InsertLines .CountOfLines + 1, "Sub... End Sub"
End With
So to add to the "MyModuleHere" code module (assuming you have a module named that), drop this in:
Sub addcode()
Dim subtext As String
subtext = "Sub PrintStuff" & vbCrLf & "msgbox ""Hello World""" & vbCrLf & "End Sub"
With Workbooks(ThisWorkbook.Name).VBProject.VBComponents("MyModuleHere").CodeModule
.InsertLines .CountOfLines + 1, subtext
End With
End Sub
As usual, CPearson adds some really useful insight:
http://www.cpearson.com/excel/vbe.aspx
With regard to removing code, which I think you're hinting at in your comment, I use the below function to find a sub name, and remove it (this assumes that I will know the length of the sub):
Function ClearModule(strShapeName As String)
Dim start As Long
Dim Lines As Long
Dim i As Variant, a As Variant
With Workbooks(ThisWorkbook.Name).VBProject.VBComponents("MyModuleHere").CodeModule
For i = .CountOfLines To 1 Step -1
If Left(.Lines(i, 1), 8 + Len(strShapeName)) = "Sub " & strShapeName & "_Cli" Then
.DeleteLines i, 6
End If
Next
End With
End Function

Answer 2

Here you have more or less all variations which, hopefully, will solve your problem. To test this code copy all of it in a normal code module (by default "Module1") Rename it as "Remin" and write "FirstMacro" in cell A1 of the worksheet you activate, a number in cell A2. Then run the first of the following procedures directly from the VBE window.
Sub SelectMacroToRun()
' 04 Apr 2017
Dim MacroName As String
Dim Arg1 As String
Dim Outcome As Long
With ActiveSheet
MacroName = .Cells(1, 1).Value
Arg1 = .Cells(2, 1).Value
End With
On Error Resume Next
Outcome = Application.Run(ActiveSheet.name & "." & MacroName, Arg1)
If Err Then
MsgBox "The macro """ & MacroName & """ wasn't found", _
vbInformation, "Error message"
Else
If Outcome <> xlNone Then MsgBox "Outcome = " & Outcome
End If
End Sub
Private Function FirstMacro(Optional ByVal Dummy As String) As Long
MsgBox "First Macro"
FirstMacro = xlNone
End Function
Private Function SecondMacro(Arg1 As Long) As Long
MsgBox "Second Macro" & vbCr & _
"Argument is " & Arg1
SecondMacro = Arg1 * 111
End Function
The code will run the FirstMacro, reading the name from the worksheet. Change that name to "SecondMacro" to call the second macro instead. The second macro requires an argument, the first only accepts it and does nothing with it. You don't need to pass any argument, but this code shows how to pass (as many as you want, comma separated) and it also shows how to ignore it - the argument is passed to a dummy variable in the FirstMacro, and the function also returns nothing.
Application.Run "Remin" & MacroName, Arg1
Would just run the macro (it could be a sub). Omit the argument if you don't want to pass an argument. "Remin" is the name of the code sheet where the called macro resides. This name could be extended to include the name of another workbook. However, if the called macro isn't in the same module as the caller it can't be Private.