I'm afraid I honestly don't know. I would imagine printing it is OK, but that writing it in some golden ink or something would be better, but I can't say for sure. I also suspect one might need to perform some sort of rite to authentic or empower the amulet, but I'm not sure about that either. Maybe Malcolm would know? Anyone out there in regular contact with a knowledgeable lama they can ask?
Also, are you particularly interested in making an amulet, or would you be interested in purchasing one from a monastery? I ask because mahasiddha.org (connected with Kyabje Do Drupchen Rinpoche's monastery in Sikkim) sells a multitude of amulets made by monks at Do Drupchen Rinpoche's Chorten Gompa in Sikkim. Either way, hope you find the answers you need.