The boss made a schedule change.

For some reason, the boss made a schedule change.

A.

inverted the subject-verb order

B.

changed sentence to a compound sentence

C.

combined two independent clauses

D.

added a prepositional phrase

The change made in the second sentence given is that, it was added with a prepositional phrase. The prepositional phrase is "for some reason". The preposition here is the word "for". A prepositional phrase is used as a modifier that consists of a preposition and the object.