I need to load a custom module and bring a link up manually
That is normal. See
https://pascal-walter.blogspot.com/2015/08/installing-lawicel-canusb-on-linux.htmlI'm attached on a one-to-one basis to a device with documented addresses, and I need to read and possibly write some of those. Any suggestions would be appreciated
Install can-utils. Although there are other tools you can find if you search through my older messages in this thread, everything needed is already there. It is best if you have CAN messaging docs for your devices, but CAN hacking is not that hard, either. In hacking you try to physically change something on your device and while spying CAN network you try to interpret data changes you see in the messages (CAN data messages are usually heavily bit packed records with no bits wasted and no byte alignment). Without docs it will be hard to guess how to send data to device, so it might be helpful to already have a device which writes to target device. Then all you need is to spy those messages and simply replicate them or try to guess the message data structure when you need to have a variable parameter.
Here is some real life example. Let's say that you're lucky and in your car you have a button without any function attached to it, and you are not satisfied with just 2 speeds for your rain wiper blades. You need to spy the vehicle CAN network (usually there are more CAN networks then just one you access through OBD-II interface), and then look for new messages, or changes in existing messages when you press that button. Then you spy for message which shows when you press button for a single manual rain wiper blade cycle. Now, you should have everything needed to write a program which waits for a single, double, or long click on unused button to set custom interval which will be used for commanding rain wiper blades, and increase or decrease it in case of a need. When everything works the way you want on your Pi, you can program some Arduino like board and leave your custom device permanently in the car.
Happy you, problem solved!
Now imagine other ideas like protecting your vehicle start up with morse like taps on a button. Sky is the limit.... Have fun!
PS: If you do not have unused button in your car, you will probably be able to find a button to which you can safely add double, triple or long click. There are even cheap wireless bluetooth multimedia buttons which you can attach to your wheel or on your dashboard. They can be used as custom additional buttons for your bluetooth Arduino (all ESP microcontrollers have BT) when you can not find any unused button in your car.