No you cannot make your own custom sized buttons, but you can change their sizes.
The ability to change button sizes in each panel was added with Launcher version 2.5. Previous versions do not support this feature.
Changing Launcher Button Size:
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Step 1
Hold down the Command key and press the mouse button while the pointer is over a section of the background pattern in the Launcher window.
Step 2
A menu will appear, with the choices of small buttons, medium buttons, or large buttons.
Step 3
Select the desired size and release the mouse button and the Command key.
NOTE: To change each panel to the same button size, you must change each panel individually. Each panel is independent of the others.
Article Change History:
21 Dec 1995 - Added information on panel independence.
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