In the past, several users wanted the ability to tell Serendipity that specific markup plugins shall not be applied to specific entries.
Until now, Serendipity applied markup plugins globally to every entry, without any distinction. Today I have committed a patch that enhances the "Extended options of Entries" plugin to specify, if specific markup plugins should NOT be applied to an entry.
This now enables you to create entries where you don't want to use the nl2br or Wiki markup. Plus, with some basic coding skills you can add new markup plugins which don't affect past entries, if you create the required entryproperty for those past entries that disable the markup plugin.
The feature has been committed to the SVN 1.1-alpha trunk and also to the affected plugins in our Spartacus repository. The change is backwards compatible, so nothing will change if you either don't use the functionality or do not make any settings to the list of disabled markups.