Yes, if you have smaller sections of a design that fit together to make a larger design you can easily combine them into the larger design using BuzzEdit.  As hoop sizes get larger, this is a great way to simplify your stitching time at the machine.

To do this:

1. Open the original design into BuzzEdit.
2. Convert Format if Needed: To convert formats use BuzzTools > Convert Embroidery Design.
3. Change Hoop if Needed: To change your hoop, use View > Hoop Properties.
4. Combine: Use File > Insert Design to select the stitch file you wish to combine with the one you have open. Choose to insert at the end of the design to ensure that these stitches stitch after the first. The stitches will be placed at the end of the design, but it will be centered in the hoop of the current design. While it is still selected in SPACE, drag it in the hoop until it is lined up with the original design.
5. If desired, use BuzzTools > Center > Both to center the design in the hoop. You can also use BuzzTools > Sort Colors to combine duplicate colors, as you would any other design.

6. Use File > Save As to save a copy of the design using a new name.

Be sure to run the sew simulator and do a test stitch out before you sew onto your garment to verify design placement and to make sure no under stitching was accidentally moved on top of filled regions when the colors were sorted.