Hello James,
If you need to split the big point cloud into smaller tiles, then just use Split in blocks option in the Export Point Cloud dialog.
In case you have different areas of interest, then your request can be completed using custom Python script that will export points based on polygonal shapes that have been pre-loaded (imported) to the project. If you need assistance with the latter option, providing that you can import or draw polygonal shapes in the project corresponding to the areas of interest, please let me know.