How to configure PG text search dictionary through sql
By design (it's hardcoded) tsearch_data directory is in SHAREDIR. If you want to change SHAREDIR you should use your own compiled version of PostgreSQL. If you are interested, you can read the documentations' Installation from Source Code section and If you still want to change tsearch_data, well PostgreSQL is opensource, you can change Makefile and ts_utils.c and again have your own version of PostgreSQL by compiling it. 

You can also use symbolic link.