Yes. You can customize the template of a board in these 2 ways.
1.By changing the board settings: The settings icon is located on the top right of the board. image.png 62.44 KBUsing this option you can modify collage height, border, and space between images.
2. By hovering over the empty space between the images: You will see a pink selection as shown below,2017-05-11_11-28-48.png 73.15 KBClicking and dragging this pink selection will allow you to modify the size of each cell vertically and horizontally.