1 - Either with Transform tool or by nudging a part of it (Transform tool can cause blurred edges with raster objects)
2 - There's a pull-down menu at the top toolbar, just right of the Custom Shape Tool - if you open this menu, there's a "Fixed Size" option.
Another way to achieve it is by filling a selection with required dimensions (which can also be set entered into the fields at the top toolbar when using a Marquee selection tool).
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