Similar to Update Constraint Names, but this changes key constraint, fk constraint, check constraint, lob storage names regardless of whether they are still using their default names.  
It tries not to rename them subsequently though. 

1) bring up the Script Explorer

2) right click on "User Defined" and select "New Script"

3) copy/paste the script below into the edit control

4) hit the run button (the first icon in the toolbar above the edit control)

Note: you can undo/redo the effects of this script as with any Model changes


/********** start of script *************/

Function CheckNameIsUniqueAcrossColumns(Parent, ChildType, ForChild, Name, Document, PropName)
	Dim Table
	Set Table = Parent
	If Parent.TypeName = "Column" Then
		Set Table = Parent.Owner
	End If
	Dim Columns
	Dim Column
	Set Columns = Table.Children("Column")

	For Each Column in Columns
		If Not NameIsUnique(Column, ChildType, ForChild, Name, Document, PropName) Then
			CheckNameIsUniqueAcrossColumns = False
			Exit Function
		End If
	Next
	If ChildType = "Check Constraint" Then
		If Not NameIsUnique(Table, ChildType, ForChild, Name, Document, PropName) Then
			CheckNameIsUniqueAcrossColumns = False
			Exit Function
		End If
	End If
	CheckNameIsUniqueAcrossColumns = True
End Function


Function NameIsUnique(Parent, ChildType, ForChild, Name, Document, PropName)
	Dim Children
	Dim Child
	Set Children = Parent.Children(ChildType)
	For Each Child in Children
	    Continue = True
	    If ChildType = "Index" And Child.HasProperty("Key") Then
	        Continue = False
	    End If
	    If Continue Then
			If Not Child.Equals(ForChild) And Child.HasProperty(PropName) Then
				If Child.Property(PropName).AsString = Name Then
					NameIsUnique = False
					Exit Function
				End If
			End If
	    End If
	Next
	NameIsUnique = True
End Function

Sub RenameChildren(Parent, ChildType, Prefix, ParentName, Framework, ByRef Num, Document, PropName, ByRef AltNum)
	Dim PropertyValue
	Set p = Framework.CreatePropertyValue(ChildType, "Generate Name")
	p.FromBoolean(True)
	Dim Children
	Dim Child
	Set Children = Parent.Children(ChildType)
	For Each Child in Children
	    Continue = True
	    If ChildType = "Index" And Child.HasProperty("Key") Then
	        Continue = False
	    End If
	    If Continue Then
			Do
				UseAltCounter = false
				UsePrefix = Prefix
				OldName = ""
				If Child.HasProperty(PropName) Then
					OldName = Child.Property(PropName).AsString
				End If
	            If ChildType = "Key Constraint" Then
				    If Child.Property("Type").AsString = "Primary" Then
						UsePrefix = "PK"
				    Else
						UsePrefix = "UQ"
			        End If
		        End If
				If ChildType = "Check Constraint" Then
					If Child.Property("Type").AsString = "NotNull" Then
						UsePrefix = "NN"
						UseAltCounter = true
					End If
				End If
	            NewName = UsePrefix
				If UsePrefix <> "PK" Then
					If UseAltCounter Then
						AltNum = AltNum + 1
						NumToUse = AltNum
					Else
						Num = Num + 1
						NumToUse = Num
					End If
		        	If Len(NumToUse) = 1 Then
			        	NewName = NewName & "0"
		        	End If
		        	NewName = NewName & NumToUse
				End If
				NewName = NewName & "_" & ParentName
		        NewName = Replace(NewName, ".", "_")
		        NewName = UCase(Left(NewName, 30))
				If Len(NewName) = 30 And Right(NewName, 1) = "_" Then
					NewName = Left(NewName, 29)
				End If
				If ChildType = "Check Constraint" Or ChildType = "Lob Storage" Then
					UniqueName = CheckNameIsUniqueAcrossColumns(Parent, ChildType, Child, NewName, Document, PropName)
				Else
					UniqueName = NameIsUnique(Parent, ChildType, Child, NewName, Document, PropName)
				End If
			Loop While Not UniqueName
	        If NewName <> OldName Then
		        Document.Write(vbTab & "Changing " & ChildType & " " & PropName & " " & ParentName &  "." & OldName & " to " & NewName & vbLf)
				Set pName = Framework.CreatePropertyValue(ChildType, PropName)
				pName.FromString(NewName)
		        Call Child.SetProperty(PropName, pName)
 	        End If
			Call Child.SetProperty("Generate Name", p)
	    End If
	Next
End Sub


Sub RenameChildTypes(Table, Document, Framework)
	TableName = Table.Property("Name").AsString

	' rename column LOB storage clauses

	Dim Columns
	Dim Column
	Dim Clause
	Dim Num
	Dim AltNum
	Set Columns = Table.Children("Column")
	Num = 0
	AltNum = 0
	For Each Column in Columns
		Call RenameChildren(Column, "Lob Storage", "LOB", TableName, Framework, Num, Document, "Name", AltNum)
	Next

	Num = 0
	AltNum = 0
	For Each Column in Columns
		Call RenameChildren(Column, "Lob Storage", "LX", TableName, Framework, Num, Document, "Index Name", AltNum)
	Next
	' Run check constraints back to back and keep num incrementing

	Num = 0
	AltNum = 0
	For Each Column in Columns
		Call RenameChildren(Column, "Check Constraint", "CK", TableName, Framework, Num, Document, "Name", AltNum)
	Next
	Call RenameChildren(Table, "Check Constraint", "CK", TableName, Framework, Num, Document, "Name", AltNum)

	Num = 0
	Call RenameChildren(Table, "Index", "IX", TableName, Framework, Num, Document, "Name", AltNum)

	Num = 0
	Call RenameChildren(Table, "Key Constraint", PrePrefix, TableName, Framework, Num, Document, "Name", AltNum)

	Num = 0
	Call RenameChildren(Table, "Relation", "FK", TableName, Framework, Num, Document, "Name", AltNum)
End Sub

Sub Evaluate_OnLoad()
	Set Context = CreateObject("SCF.ScriptContext")
	Set Document = Context.ScriptDocument
	Set ThisScript = Context.Object
	Set Options = Context.Options
	Set Model = ThisScript.Model
	Set Framework = CreateObject("SCF.ScriptFramework")
	Document.Write("Updating Model " & Model.AsObject.Property("Name").AsString & " Constraint Names..." & vbLf)
	Model.BeginTransaction("Change Constraint Names")
	Set Tables = Model.AsObject.Children("Table")
	For Each Table In Tables
		Call RenameChildTypes(Table, Document, Framework)
	Next
	Model.EndTransaction()
	Document.Write("Updating Model " & Model.AsObject.Property("Name").AsString & " Done!" & vbLf)
End Sub