How to use a Orange Pi R1 (dual ethernet) to invisibly sit between a printer and a router and sniff/alter data that is sent?

Hello,

I've been working on this project for quite some time and keep getting stumped. I want to create a device that lets you capture and possibly alter the data getting passed through the device to a printer.

Device: Orange Pi R1

OS: Armbian Bionic

Network/Router <--eth0--> Orange Pi R1 <--eth1--> Printer

I have found many tutorials on creating sniffers, but after following many of them I can't seem to get it to work. All the tuts are a bit old and they don't bring up network manager at all so I'm not even sure if I'm disabling that correctly so I can use interfaces. I'm not even sure if I am going down the right path here. I'm assuming that I create a bridge between eth0 and eth1 and then have wireshark or tcpdump look at that bridge for sniffing. I then thought I could use IPtables to route print jobs (port 9100) for processing and then send them to the printer.

I want the printer to be able to choose it's IP or use dhcp (whatever the printer settings are) and the router/network will see it the printer. The device should be invisible to the network. I really could use some help, happy to gilde for a point in the right direction.

Thanks guys