[Orgmode] exec code on task state progression

[Richard Riley]

What would be the best approach, if at all possible, to having org
manage tasks which allow me set dates for a task to be scheduled and
then let me manually progress/cycle that task and have it then invoke
code/scripts?

e.g I might have a task which is "Update Org" which is scheduled as a
repeat task once a week, When marking it done for that week (to drop it
from my agenda) it also runs a shell script which goes ahead and
executes a small bash script which does a git pull etc. I might also use
it for, say, reminding me to send an email to certain customers every
month and actually invoke the necessary gnus functions via elisp when I
set it to "done".

I realise I can use babel to manually exec code blocks and that org can
also follow shell and elisp links, but how to easily tie that in with
task flow?