If mode is set at 0, the bmap size is unchanged. If the image file size is different, or is not a power of 2, parts of the image can be clipped away or filled with black.If mode is set at 1, the bmap is changed to the new size. It must be a power of two in size.

from the manual.

I am not sure if bmap_load will work for full screen size panel. Because the image would not have the power of 2.

I already use bmap purge for deleting the images from the start menu. This is working fine.

Do you have a small example how to change the current image on a panel with a new one from the folder? With the right size? I mean a full screen panel with a 1280 x 720 px image.