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.