deface

To damage or vandalize something, especially a surface, in a visible or conspicuous manner.

1869: George Eliot, The Legend of Jubal That wondrous frame where melody began / Lay as a tomb defaced that no eye cared to scan.

After the painting was defaced a decade ago, it went viral and has been a tourist attraction ever since.

To void or devalue; to nullify or degrade the face value of.

He defaced the I.O.U. notes by scrawling "void" over them.

1776: Adam Smith, The Wealth of Nations One-and-twenty worn and defaced shillings, however, were considered as equivalent to a guinea, which perhaps, indeed, was worn and defaced too, but seldom so much so.

To alter a coat of arms or a flag by adding an element to it.

You get the Finnish state flag by defacing the national flag with the state coat of arms placed in the middle of the cross.