Change one word

[Lumen]

Patrol Guard

[LamBear*]

Guard rail

[Lumen]

Off Guard

[HL1]

Trade Off

[Lumen]

Fair Trade

[HL1]

Fair Warning

[Perfect Warrior]

Vanity Fair

[Lumen]

Fair Maid

[Neffy]

House Maid

[Lumen]

Bird house

[Colleengael]

Bird bath

[Lumen]

Oh, of course ..

Just replace one of the two words with another one. It doesn't matter which word you remove and you could add the new word either before or after the remaining word as long as the two words make sense when used together.
For example: bird feathers

[Neffy]

Can you give an example ?

[Lumen]

Duck feathers