I have 4 yucca plants that have never been pruned. Can I prune them safely, and if so how?

They won't die even if you prune them hard. If they are real Yucca. Some things that look like yuccas don't handle the stress of prunning so well.

Not sure what pruning you are planning. I have tip pruned leaves and cut some back nearly to nothing. They continue to grow fine. But they do look odd for a year or 2.

Or are you talking about taking off the dead leaves. They can be removed. But they are there to protect the plant from hot sun and help keep the soil moister.

Very strong gloves, thick sleeves,and remove the bottom leaves until they are all good looking ones.

Don't tip prune.

You can cut the big center stem (at an angle) down close to the ground.