Also, I have corrected the borders to the west and northwest, so it should be possible to build a straight wall, like shown on the images and yes, the wall at the waterside is only to show the actual size of the area, it doesn't make any sense besides that ;-)
No known issues, but maybe you will be noticed to leave the buildable area, when running around at the west side, since the area contains several areas and the overlapping isn't perfect - just do a few steps left or right and you're fine.
No cell reset caused by this mod, only by the game itself and it should work with mods that are using reconstructions of the farm house.
If it should happen, that the area seems to be still the same, look at my a-i-o mod, cause there is a solution for cases like that.
Thanks to bill8872 , I can provide you with a solution for the "shrunken build area"-issue.
Like he was stating in the bugs section: open the console and type in "resetquest patch_1_6" , without the quotes, and you should be able to use the whole area again - I have tested it with Jamaica Plains and my expansion was back in full effect !
In case that this won't work, cause the console is showing that the "reset" command is not recognized by the game, instead just use "quest patch_1_6", or "patch_1_6" without the quotes.