From Longman Dictionary of Contemporary Englishtack something ↔ on phrasal verbADDto add something new to something that is already complete, especially in a way that looks wrong or spoils the original thing a beautiful old house with a hideous modern extension tacked on at the back → tack→ See Verb table
Examples from the Corpus
tack on• The Vice-President, Richard M.. Nixon, then tried an-other tack.• To the left of the map pictures of Paula Wilson, plus the remains of the two dead murderers, were tacked.• There beside him, tacked up on a long corkboard and framed inn glass, were the familiar pages of the Tribune.• In the spring, you could tack them on a post in your garden to keep the crows. away!• Let the samples dry thoroughly, then tack them up on a wall and note the differences.• I washed it and soaked it best I could and tacked it on for the back of the skirt.• Questions about the nature of the self have taken different tacks depending on which tradition the questions come from. 