It is hardcoded in the create_climfile.m, create_inifile.m and create_bryfile files.
mosa@parti-mosa:~/croco_tools-master/Preprocessing_tools$ grep Vstretch *
create_bryfile.m:nc{'Vstretching'} = ncint('one') ;
create_bryfile.m:nc{'Vstretching'}.long_name = ncchar('vertical terrain-following stretching function');
create_bryfile.m:nc{'Vstretching'}.long_name = 'vertical terrain-following stretching function';
create_bryfile.m:nc{'Vstretching'}(:)=1;
create_climfile.m:nc{'Vstretching'} = ncint('one') ;
create_climfile.m:nc{'Vstretching'}.long_name = ncchar('vertical terrain-following stretching function');
create_climfile.m:nc{'Vstretching'}.long_name = 'vertical terrain-following stretching function';
create_climfile.m:nc{'Vstretching'}(:)=1;
create_inifile.m:nc{'Vstretching'} = ncint('one') ;
create_inifile.m:nc{'Vstretching'}.long_name = ncchar('vertical terrain-following stretching function');
create_inifile.m:nc{'Vstretching'}.long_name = 'vertical terrain-following stretching function';
create_inifile.m:nc{'Vstretching'}(:)=1;
These are located in the Preprocessing_tools directory of CROCO_TOOLS