Let's assume we have Autoconf's build system-based application with a preexisting recipe for it, and we want to do the following:

The content of the .bbappend file, in order to make the changes, will be the following:

EXTRA_OECONF += "--enable-my-feature --disable-another-feature" 
EXTRA_OEMAKE += "DEFINE_PASSED_TO_MAKE=1" 

The same can also be done based on the hardware we are building for, as follows:

EXTRA_OECONF_append_arm = " --enable-my-arm-feature" 
EXTRA_OEMAKE_append_mymachine = " MYMACHINE_SPECIFIC=1"