alter server for foreign table

According to Postgresql documentation it is not possible to alter server
for foreign table:

https://www.postgresql.org/docs/10/static/sql-alterforeigntable.html

But stackoverflow suggests the following hack directly updating
|pg_foreign_table|:
https://stackoverflow.com/questions/37388756/may-i-alter-server-for-foreign-table

I wonder how safe it is and if it is so simple, why it is not support in
ALTER FOREIGN TABLE statement?

Thanks in advance,

--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company