General Overriding:
* Preempt
* Supersede
* Overrule
* Disregard
* Ignore
* Trump
* Cancel
* Invalidate
In a Computer Context:
* Bypass
* Overwrite
* Replace
* Supersede
In a Legal Context:
* Overrule
* Reverse
* Set aside
* Vacate
In a Control Context:
* Subdue
* Suppress
* Overpower
The best synonym for "override" will depend on the specific situation and the intended meaning.