This is completely different and much more complex request. To achieve functionality I am askin gfor, they have just add a new settings for 'always be able to edit first post' and when checking, if user is allowed to edit post skip checks of 'time, while allowed to edit' setting. No need to add wiki functionality, just a small tune for posts editing time settings, which are already in core.

I made some fixes to the composer for disabled categories, will be available in next release. Thanks for reporting.