I'm wondering aloud if the conceptual change from 18 to 27 implies that the Old Tom Morris course, with the old first 9 along the valley and the back 9 now mostly the Coastguard 9 were left intact, and 9 new holes were to compliment the 9 newer holes between the road and the Sandy Hills course, while the other 18 were to be their own course.
I'm not sure I followed what you were asking here.
The old Coastguard nine has been altered to eliminate a couple of road crossings, although it still does have one hole where you hit the second shot over a less-traveled road. Also, I think one of the old holes has been abandoned for real estate. I don't think there is any thought of returning that nine to the main course.
Additionally, the new front nine of the Valley course [the Old Tom Morris course] is kind of landlocked between the road, Sandy Hills, and farmland that is tied up in a Special Area of Conservation. There's no way to build a new nine and connect it to that one.
Our solution is to build a totally new 18-hole course on the St. Patrick's land.
There will still be plenty of ground left over [most of it on the big dune / hill ] if they also want to pursue a par-3 course or something like that down the line . . . but in fact they already have something like that along the road, which looks pretty cool, though I have never got out on it to play.