Here is experimental code to set (hide = True) or clear (hide = False) the hidden design flag. This is no different in its effect from using a hex editor on the NSF. With either method you might have to fiddle about to get the new setting recognized -- it must be cached somewhere. Making a trivial change to the replication settings often works.
Const APIModule = "NNOTES" ' Windows/32 only
Const REPLFLG_HIDDEN_DESIGN = &H0020
Type ReplicaInfo
ID(1) As Long
Flags As Integer
CutoffDays As Integer
CutoffDate(1) As Long
End Type
Declare Function NSFDbOpen Lib APIModule Alias "NSFDbOpen" _
( Byval P As String, H As Long) As Integer
Declare Function NSFDbClose Lib APIModule Alias "NSFDbClose" _
( Byval H As Long) As Integer
Declare Function OSPathNetConstruct Lib APIModule Alias "OSPathNetConstruct" _
( Byval Z As Long, Byval S As String, Byval F As String, Byval P As String) As Integer
Declare Function NSFDbReplicaInfoGet Lib APIModule Alias "NSFDbReplicaInfoGet" _
( Byval H As Long, R As ReplicaInfo) As Integer
Declare Function NSFDbReplicaInfoSet Lib APIModule Alias "NSFDbReplicaInfoSet" _
( Byval H As Long, R As ReplicaInfo) As Integer
Sub HideDesign(db As NotesDatabase, hide As Variant)
Dim hDB As Long
p$ = Space(256)
OSPathNetConstruct 0, db.Server, db.FilePath, p$
NSFDbOpen p$, hDB
Dim R As ReplicaInfo
NSFDbReplicaInfoGet hDB, R
If hide Then
R.Flags = R.Flags Or REPLFLG_HIDDEN_DESIGN
Else
R.Flags = R.Flags And Not REPLFLG_HIDDEN_DESIGN
End If
NSFDbReplicaInfoSet hDB, R
NSFDbClose hDB
End Sub