I have been able to change the boot animation of one theme and use a another theme's boot animation with no problem. As far as lockscreens are concerned if have been able to do that as well. The way I have been able to change both is through theme manager, and then tapping on the edit themes option.
Under edit theme you can even change the font to be a font from another theme that you like. Even the way your SMS is setup.
If you like how a themes folders/menu screens look but would like to have different icons, this is possible as well.
Just experiment with it and find something you like. Theme Manager, and at the top you will see the option to "Edit Theme. "
Hope this helps.
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