Can one add further source files to an executable once defined?

Given I have defined an executable with its main source file in a CMakeList.txt file:

ADD_EXECUTABLE(MyExampleApp main.cpp)

Can I add further source files to this executable after this line but in the same or an included CMakeList.txt file?

What is a executable target?

An IMPORTED executable target references an executable file located outside the project. No rules are generated to build it, and the IMPORTED target property is True . The target name has scope in the directory in which it is created and below, but the GLOBAL option extends visibility.

Use target_sources, available since cmake 3.1

eg. target_sources(MyExampleApp PRIVATE ${extra_file})

https://cmake.org/cmake/help/v3.1/command/target_sources.html