Learn Spanish (Latin America): Mi colega acababa de intercambiar dos teclas en el teclado. - My colleague had just swapped two keys on the keyboard.

The phrase acabar de + infinitive is almost always used in either the present or the imperfect tense. In the present (acaba de intercambiar), it means "has just swapped". In the imperfect (acababa de intercambiar), it sets the background for a past event, meaning "had just swapped". Using the preterite (acabó de...) would literally mean "finished swapping," which loses the idiomatic "had just" meaning.

Why use intercambiar instead of just cambiar?

intercambiar specifically means "to swap" or "to exchange" things with each other (like switching the position of two keys). cambiar is broader and usually means "to change" or "to replace". If the colleague simply put entirely new keys on the board, you would use cambiar.

I learned that "key" is llave. Why is tecla used here?

In Spanish, a key to unlock a door is a llave. However, a key on a computer keyboard, typewriter, or musical instrument (like a piano) is a tecla. Naturally, a collection of these makes up the teclado (keyboard).

Is colega a masculine or feminine noun?