In the strict definition, yes..
"Defacing" would be the addition of a symbol or charge to another flag.
In the United States it is against the Flag Code to deface the national flag with advertising or with any other sigil, image or insignia.
With that said, it is done all the time. I do (an opinion) believe it is very different than Flag Desecration.
In vexillology "defacing" does not carry negative connotations..