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

Question

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

ADD_EXECUTABLE(MyExampleApp main.cpp)

Can I

Answer 1

It should be noted that for more recent versions of CMake (> 3.1 I think) one can append files to the SOURCES property on targets.

http://www.cmake.org/cmake/help/v3.3/prop_tgt/SOURCES.html