Just pick exercises you like and that's it.
The program is there to make you think which exercises are most effective.
The exercises you choose are for you and your goals. Nobody else.
Or, as the book says: Find your Kroc Row.
Here's on I like:
Press downs/Face pulls
What is Squat deload?
Triumvirate = 3, so as outlined by Jim's template, three exercises per workout - one core lift + 2 assistance exercises of your choice.
You do the program as written, with no modifications. Use the 5/3/1 template for each of your four core lifts, and on each core lift day, do, say, 2 different assistance exercises that support your goals. The options for assistance work are laid out in the Beyond 5/3/1 book. Do one or two exercises for five sets of 10, or maybe do a few more exercises for fewer sets. For example, if you want to work your core, you could pick hanging leg raises as an assistance exercise on your deadlift day, along with, say, Good Mornings to work the hamstrings and glutes. If you want to focus on something else, pick two different assistance exercises. You customize your assistance work to suit your goals, but that's the "triumvirate" template.
I squat using the deload weight. I have found some light squats before dead lift really helps me.
I started a cycle of programming using the "Triumvirate" template 3 weeks ago. This next week will be my 4th and my deload week. I like it so far because it's simple and keeps me from doing too much. I created a training log in the forums titled "Giving 5/3/1 a try". Check it out if you are interested in seeing what kind of progress is to be made. I dont have the book and have included some other exercises to help meet my own personal goals but havent strayed too far from the original program. You might be interested the assistance exercises I have thrown into the mix.