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In many design applications, by deleting sublayers (or child layers) the main parent layer will still remain intact.
You can unlock or unhide all objects at once by typing CMD + / or CTRL + / (depending on your platform).
When renaming layers you can hit TAB to skip quickly to the next one. Hitting SHIFT + TAB will take you back up the list, renaming as you go.
To expand multiple layers at once, start by selecting the layers you want in the layers panel to the left.
To quickly lock a whole bunch of layers in Figma, just click a layer “lock” icon and drag down until you’ve locked all you need (the same applies in reverse for unlocking layers).