Actually according to UEFA Stadium Regulations 2006 Article 16. Point 2 reads:
The use of temporary stands is prohibited.
Although point 1 of the same article would put our O'Donnell Stand (North and South) out of use as it reads:
Seats for spectators must be individual, fixed (e.g. to the floor), separated from one
another, shaped, numbered, made of an unbreakable and non-flammable material
and have a backrest of a minimum height of 30 cm when measured from the seat
Although again same Article, if I read this right Terracing is allowed in the First Qualifying Round... Unless they have changed where it says Round 2, now reads round 1.