Not sure if Badspot prefers that you not modify the folder contents, but...
Go to this section of your Blockland folder...
C:\Users\"Username here"\Documents\Blockland\base\data\shapes\
Then find the file named "brickTOP"...
Copy this file, or don't (Up to you), as a backup, then replace it with the new image that you'd prefer. In your case, make it the Lego stud. The image has to be identical, so same Height, Width, Transparency, etc. Obviously it also should be the same image format as well.
Then make sure to go to the image properties, and check "Read-Only" so the game doesn't overwrite the file.