One .inc file included in some image-.bb file defines shell function for Bitbake task.
Let's concentrate here merely on this shell function, asigned Bitbake task is out of scope.
I wonder how to undefine this shell function in .bbappend file (other layer).
unset -f <shell-function-name>
is not working
ERROR: ParseError at .......-image.bbappend:89: unparsed line: 'unset -f do_thisandthat'
Does it need be said Bitbake explicitely "unset -f < shell-function-name>" is a shell script?
Me consulted for this question Bitbake Manual and Yocto Project Reference Manual with outcome of zero findings.
There is no direct API for it however you can do something like:
which will delete the shell function since functions are simply variables.
Just deleting a function may well cause other problems but that does answer your specific question.
This is an 'anonymous python' fragment and will be executed by bitbake at the end of parsing a recipe (or bbappend to a recipe).