Desecrating a national flag is considered a crime in many countries. I think that’s stupid. A flag, in the physical sense, is nothing more than cloth or similar material. Desecrating it hurts no one because even a person with a phobia of desecrated flags is only affected by his or her psychological condition, so I don’t think it should be a crime unless the flag is someone else’s personal property and that person, or those people, never gave you permission to desecrate it.
A flag is just clothe with a pattern. Do what you want to it.