Can I customize the launchpad grid?
Yes, this is totally possible, assuming you're okay to run some terminal commands.

Follow these steps:


Launch Terminal (usually found in Applications > Utilities)
First enter the following command (just copy and paste it) and press enter:

defaults write com.apple.dock springboard-columns -int 6
Second enter this command (just copy and paste it) and press enter:

defaults write com.apple.dock springboard-rows -int 4
Finally enter this command to quit and relaunch the Dock and Launchpad  (again, just copy and paste it and press enter):

defaults write com.apple.dock ResetLaunchPad -bool TRUE;killall Dock
Once the Dock reappears, open Launchpad 
Now you'll see a screen similar to the following:





Be patient and wait for Launchpad to reload all the apps.


Now you'll have a 6 x 4 grid. You can also change the values at the end of the commands at Steps 2 and 3 to other values.

Finally, if you'd like to restore the defaults, you can run the same commands again and replace the values with the original 7 columns and 5 rows. Remember to also run the command at Step 4 whenever you make changes.