There are two geoprocessing tools in the Geodatabase Admin tool box: Create and Delete Database Sequence. You can get access to a sequence's properties using arcpy.ListDatabaseSquences.
The database sequence help page states: DatabaseSequence objects cannot be initialized directly and the properties table shows all the properties as read only.
I guess the only way to alter an existing database sequence is to delete it and recreate it. It would be cool if an existing one could be altered or modified.