I asked this question in a previous post but never received an answer I could realize.
I'm working in a PE, so I don't have Apex and can only work with standard controllers.
I had to create a VfP for the "New Lead"-page, reason being the need for a few lines of jscript added, before the creation of the Lead. Now Duplicate Rules won't work properly. When I try to save a dupe I get the proper Error but there is no way to ignore or merge it, so I either have to deactivate the message or I'm stuck in the creation.