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nablstd - Kovid has acknowledge there are a couple of mistakes, I'm sure they'll be fixed in next release.
Meantime the attached zip contains all the icons from version 2.62. You can override individual icons by putting replacements (using the same name) in the
%appdata#\calibre\resources\images\ folder, you may need to create it. The ones you're after are trash.png and tweak.png

So copy them into that folder - don't copy them into the installation folder, if only because it's bad practice to mess with such folders.
Curious - I've seen reference to "the Create New Theme" feature, where do I find it.
BR