You sure can do what you are asking. You need to get a copy of Filemaker Pro Advanced though. With that, you can create custom menus and have them active for specific layouts. It is worth the cost of admission if you do a lot of scripting too. The debug feature for scripts is a must for a serious developer.
Okay, that's not a problem. However, I just tried my app agains Filemaker Go and was very impressed. In Filemaker Go, I do not have access to the custom menus. Also, I want to keep modify on the layout, just disable new record.
I am still reading up on filemaker Go myself, but it is my understanding that you can, in a limited way, use custom menus with GO. You can, for example, write a script that either does nothing or displays a message "new records cannot be created with this layout." or some such message and use custom menus to replace the new record action with your script--effectively disabling it for a specified layout.