Good afternoon. I have just gone through the mod process, not saying what I did was right, but I have heard from a filament maker that it will work and prevent damaging wear on my UM3.
The stock AA printcores cannot tolerate abrasive filaments for very long. The first thing needed is to acquire a hardened printcore. The second is a hardened feeder.
I went with a 3dSolex Hardcore printcore AND everlast nozzles with ruby or sapphire. I tend to use a 0.6 size as it seems less likely to clog, but I bought a wider range as it made sense with shipping. Ultimaker has just come out with the Print Core CC Red, specified for abrasives, but I don't know how hard that will be to get.
Likewise, the stock UM3 feeder uses drive components that cannot tolerate CF, whereas the S5 feeder is made of hardened material that can. My solution was to buy the BondTech DDG UM3 upgrade. There are two BondTech offerings, you can decide which is best, both are hardened for CF.
I have some nylon/CF on hand and am setting up to test another brand, but haven't done anything worth reporting on yet. Others here will likely have some better experience to share.
One final thought - if you decide to start out with nylon/CF as I have, you may want to invest in a filament dryer and a drybox to keep the filament as dry as possible during printing. The nylon substrate is very prone to moisture absorption and its impact on print detail and adhesion is significant- probably the only plus side of cold Canadian winters is that I can look forward to easier printing as the house humidity plummets ?
Hope this helps!