Yes they can be safely trimmed. A lot easier if someone helps you. And wrapping the chicken in a towel makes it a lot easier.
If you can see the pulp = pink flesh in the proximal nail, try not to cut that. But even carefully cutting, you may see some bleeding, so have things ready.
I went thru human toenail clippers and pet guillotine clippers and both failed. I bought scissors type nail clippers for Large Dogs and they work great.
Have styptic powder on hand so if you get bleeding it can be stopped fairly easily. Personally found a little pressure with a tissue on the tip works well enough.
** if you are unsure where the pulp is , then just take a little off at a time about a 1/4 of an inch and repeat the trimming every week or so til the nails are down to normal length.