You can edit your board's board-media.cfg file to change the partitions in your image.
To change the partitions in an image:
Open this file in a text editor and modify the various settings as required.
For example, the OMAP5 configuration file contains this partition:
[base] path=/base type=179 num_sectors=1253376 order=2
The line path=/base identifies the mountpoint for the partition. You can change the partition settings as required. For details on the various settings, see the configuration file settings list.