R116 was tracking directly to Blackrock for the last 100nm after it left Dublin, and indeed passed by Blacksod about 4nm south, still maintaining a direct track to Blackrock, then went close by Blackrock and then turned back and approached it again. It is clear R116 was consistently aiming for what we know was Blackrock.
This does not therefore look like a late change of plan to land at Blackrock following some kind of emergency.
The question is why was the acft aiming for Blackrock. One reason is that they were deliberately using it as an approach point to get visual for a VFR transit to Blacksod. But this makes little sense - why go 10nm further to let down right over a 300ft rock rather than let down over the sea just south of your prob max 100ft elevation Blacksod destination, also having a lighthouse? A second reason could be that they deliberately intended to land at Blackrock and take stock. This makes no sense either - why would you opt for a hazardous uninhabited rock with a probably too small helipad and no fuel? And anyway, you have just told Shannon you are landing at Blacksod.
The third reason is of course that they thought they were actually going to Blacksod the whole time, hence the direct track, call to Shannon, second approach, and descent to a height that would have been fine for Blacksod. But then the huge mystery is how could such a fundamental navigation error have been made, and continue to be made, by a clearly very experienced crew? FMS mis-programming would be the obvious answer for the initial mistake - and indeed Blackrock and Blacksod are, and sound, very similar. And if you actually lived in a place called Blackrock, that name would be much more familiar, particularly late at night when you're tired and rushing...... But even if this happened it is still hard to see how such an experienced crew in presumably such a well equipped modern acft with moving maps visible to both crew and cabin would not have picked up this error in good time.