There is not 'troop quality' feature in TacOps. The game assumes all troops are reasonably well trained and reasonably well lead. The only determinants of mission success are the player's skill and the difficuly of the mission chosen.
You can easily simulate inferior local forces by giving them older/lower quality equipment.
This probably has its roots in TacOps being used as an Army training tool where both sides are assumed to be well led and properly equipped. Most wargamers not already familiar with TacOps will find this omission to be somewhat perplexing, but it's not the only part of the game that suffers from this. The limited elevation and lack of a proper map/scenario editor is also frustrating. This those things were fixed in TacOps 5 it could really help give the system much needed flexibility.