In my CMake-based project, I include another library as a subdir:

list(PREPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake)
set(LIBIGL_INSTALL OFF)
include(libigl)
# cmake/libigl.cmake contains:
#include(FetchContent)
#FetchContent_Declare(
#    libigl
#    GIT_REPOSITORY https://github.com/libigl/libigl.git
#    GIT_TAG v2.5.0
#)
#FetchContent_MakeAvailable(libigl)

then my CMake builds something using libigl, and installs it.

But libigl’s CMake is installing also some Eigen header files, which I do not want.

This is happening because in libigl/cmake/recipes/external/eigen.cmake install(...) commands are added unconditionally.

Ideally I’d wrap those lines in if(EIGEN_INSTALL) ... endif(), but I have no control over that. I have control only over my CMake project.

Can I instead remove all the previously created install rules (e.g. just before adding mine)?