Twilight's Fall – a separate game. Twilight Imperium's expansions, mods and rules topics are not part of it.

Hired Guns

After a system is activated, you may choose up to 3 of your ships. Those ships are also treated as the active player's and participate in combat as their units. At the end of this tactical action, that player may replace each of those ships in the active system with their own of the same unit type. Then, remove the rest from the game board.
Nokar SellshipsFaction ability

After a system is activated, you may choose up to 3 of your ships. Those ships are also treated as the active player's and participate in combat as their units. At the end of this tactical action, that player may replace each of those ships in the active system with their own of the same unit type. Then, remove the rest from the game board.

Source: Discordant Stars