Here are a couple other options:
Dynamic blocks are available in later versions of CAD and they can be created with the block editor. Some of the parameters allow stretching the block in a predefined manner. For instance, you can create a 3 dimensional representation of a standard 2x4 board. Using the dynamic blocks options you can add a grip to one end of the board which could allow you to stretch it to standard dimensions of 4' 6' 8' etc. where it would snap to those predefined options, not stopping between. Alternately you can set it to stretch with the cursor to any dimension. It just depends on what you want it to do.
For instance, our company has one for parking spaces (Civil firm) where we can select the depth of the stall at fixed dimensions (18, 19, or 20 feet), the width at fixed dimensions (8, 9, or 10 feet) and the number of spaces by dragging different grips of the dynamic block. This block also allows single or double stacked (face to face) stalls. It is slightly faster that drawing one and offsetting it hundreds of times to lay out parking lots.
Your second option would be to use the SCALE command and scale the block in the x, y, or z direction only, by the amount you want.
At the command line enter SCALE, select the base point, enter "1,2,1" to scale by 2 in the y direction only. Alternately, select the block, invoke the PROPERTIES, and adjust the x,y,z scale of the block (scales from the insertion point).
Having dynamic blocks lets you have multiple instances of the one block with different lengths, rotations, etc. Editing the block definition of a standard block will change all instances of that block in the drawing (not always what you want to do).
Nate the Great