It takes two steps to make your right click mouse button as Enter button which you can use to repeat your previous command.
Right click on the screen and open OPTIONS.
Go to User Preferences and click on Right-click Customization.
You will get this window,check "Turn on time-sensitive right click".
It says Quick click for ENTER and longer click to display shortcut menu.
Shortcut Menu is the basic menu you get when you right click on the screen or the object when this is not checked.
This means that you can use your right click mouse button as your Enter button to repeat your command each time you want,but remember Quick click is for that,if you hold your right click longer than 250 miliseconds (you can set time which you want) it will still open Shortcut Menu.
This could be easier than using ENTER button on keyboard when you want to repeat something :)