Ouch.
Is amateur art restoration really what we want to be encouraging ? Only the uninformed or inexperienced would believe that one has a second chance at repairing and restoring most materials -- especially patinated sheet metal. Do it once, do it right: find an expert, or leave it alone.
I am late to answer but I was also having the problem in removing Paul Evans Cityscape tiles from my house and after searching a lot I called professionals ... to remove these tiles and they have done it with great ease so you should take their service.
(edited by DA - link removed - no advertising on the forum please)
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