I really wish I'd stated this in my original post so apologies for that but I'll try again. Here goes...
TAKE AWAY THE REFUND ELEMENT. NO GOLD TO BE REFUNDED.
What I'm saying is let us amend our builds - like for like Tier buildings - for a limited time.
So with this there could be NO EXPLOIT. You wouldn't be able to use any gold for anything else as there would be no gold refunded. If all you have is level 2 Tier 5 buildings then you could only swap these for other level 2 Tier 5 buildings.
The whole point is to not make it possible to be exploited. It would only be relevant to those who wanted to change their existing builds. To tweak them and make them better for their needs, be it EE, EB, OSW etc...