UPDATED 2/07/11
SageTV V7 adds a feature that allows plugins to run as part of the
graph creation
process. The zip file includes two plugins that can be placed in
%ProgramFils%\SageTV\SageTV\GraphPlugin" to assist in the graph building
and enhance playback.
SGPConfig.exe - Configuration application (screen shots
below)
ChangeRefreshRate.dll - changes the refresh rate based on
the FPS of the file as playback begins using a user defined
FPS->Refresh Rate map. It can also set the speaker config (stereo, 5.1, 7.1) based on the content playing.

GraphTweaker.dll
- Adds and blocks filters based on container and codec. It can also
disable composition (Aero) during playback. In most cases it's best to
set the filter in Sage to "Default" for any codecs that will be
overridden with this plugin.
Both
plugins use MediaInfo.dll so it must be copied as well.
main.reg
- an example of how the tool can be used to load filters by
container/codec.