Why would I want to install another netcdf library?

You don't want to install another netcdf library. In general all is taken care of by the TCCG and the libIGCM team. Nevertheless, there was a netcdf-related problem in March 2015 and this was the procedure to load a different netcdf library, use it for the compilation and use it for running the model. Check which modules are loaded

module list
}}

Unload the module you no longer want to use, i.e., netcdf/4.2_hdf5_parallel. Note that there could be dependencies between modules. If so unload whatever needs to be unloaded.
{{{
unload module netcdf/4.2_hdf5_parallel (NetCDF)
}}}

Check if the new module was loaded
{{{
module list
}}}

load module netcdf/4.3.3.1_hdf5_parallel
module show netcdf/4.3.3.1_hdf5_parallel

setenv		NETCDF_ROOT	/usr/local/netcdf-4.3.3.1_hdf5_parallel
setenv		NETCDF_EXEDIR	/usr/local/netcdf-4.3.3.1_hdf5_parallel/bin
setenv		NETCDF_INCDIR	/usr/local/netcdf-4.3.3.1_hdf5_parallel/include
setenv		NETCDF_LIBDIR	/usr/local/netcdf-4.3.3.1_hdf5_parallel/lib

../../modeles/IOIPSL/src/Makefile
../../modeles/ORCHIDEE/arch.path
../../modeles/XIOS/arch/arch-X64_CURIE.path

NETCDF_INC_DIR is deprecated and has been replaced by NETCDF_INCDIR
    NETCDF_LIB_DIR
NETCDF_INC

DIR
DIR
../../../libIGCM/libIGCM_sys/libIGCM_sys_curie.ksh