Drop sniffed packet on matching content

I have made a packet sniffer in C using rawsockets that sniffs all outgoing UDP traffic on a specified port.

I now want to drop certain outgoing UDP packets that match a certain payload, so that they can be resent with a different payload.

A sniffer will no longer be useful in this situation, because it seems unable to motify the network traffic it detects.

Is there a way to drop packets that match a certain payload and port on a Linux system without modifying kernel code? Is my sniffer useless for the goal I have?