Edit MapDifficulty.dbc to add raid mode for the instace or replace the instance mode with raid only.
Then, you need to change the value in the World DB, access_requirement table, find the map ID for Shattered Halls and then the second column (difficulty entry) (if you've replaced in MapDifficulty.dbc) or create a new row with same map ID but different difficulty entry if you've added a new difficulty in the DBC.
For instances:
0 = 5 (dungeon)
1 = 5 hc (dungeon)
For Raids:
0 = 10
1 = 25
2 = 10 hc
3 = 25 hc