I dont use them, Dave.
Unless one expects to find oneself in a situation where one is working with a knife above ground (rock climbing/in a tree/over deep water etc) and it would be a serious problem or cause possible injury to someone below you if you dropped it (or if one has a tendency to fumble knives on a fairly regular basis), its not really essential. If one uses a very deep friction fit sheath that comes almost to the top of the handle, a lanyard might be useful for removing the knife from its sheath. But this is all personal opinion.
There is no reason why you cant use the top pin hole as a lanyard hole, if the tang/liners/slabs are epoxied together. And theres no reason why you shouldnt enlarge the diameter of the top pin hole in the tang if necessary
To avoid pushing all the epoxy out of the slab/liner/tang/liner/slab arrangement when inserting the pin(s), you could cut a few grooves into the pin(s) either along the pins length or around its circumference. This will help retain some of the epoxy around the pin(s) and give the epoxy something to bite into on the smooth rod.
Best regards,
Paul.