A system, and computer program product for modifying intercepted data interactions are provided in the illustrative embodiments. At a security application executing in a security data processing system, an intercepted packet of data arranged according to a protocol is received from an intercepting agent executing in an intercepting data processing system. A security policy is applied to the intercepted packet. In an instruction according to a coding grammar, a modification of the intercepted packet is encoded. The instruction is suited for the encoding under a circumstance of the modifying. The instruction is sent to the intercepting agent. The intercepting agent at the intercepting data processing system performs the modification according to the security policy and independently of the protocol.