On most NOT all Weber grills it is not simply swap out orifices. Never was. On some it is but Weber in their infinite wisdom to confound and discourage their owners from doing conversions made sure it's not always that simple or that easy to even determine. There are videos online of people with half brains doing this and claiming it works. They should not be believed or followed. I have done a large number of these conversions for myself, friends and family so I am telling you from experience.
Please do a search on this and find posts from myself and another member who was kind enough to post photos of the different types of valves Weber has used in their grills. Though the new ones are so new and unknown I don't believe anyone knows what Weber is contracting for in China when this new line of grills is built
Bottom line most Weber grills have valves with 3 settings. Low/Med/High. Some have a continuously variable valve (like your kitchen range). The fixed valves need to be modified (or replaced) when going from LP to NG. They cannot be modified to go the other way so a manifold is called for.
The variable types in most cases can simply have the orifice changed to whatever fuel you like assuming you have the correct orifice size for the rated BTU of the burners, and the gas pressure coming in.
Confused yet?