Change archivelog location in Oracle
There are the manuals Specifying Archive Destinations,LOG_ARCHIVE_DEST_n. But they are unclear about if it is possible to change it online. 


Try it out on a test instance. You always should try out thinks on a test instance. Especially if you are using some tips from the internet.
If you an alter system set = ... scope=both; and the parameter cannot be specified in memory, you get a 



ERROR at line 1:
ORA-02095: specified initialization parameter cannot be modified


error, but nothing bad happens. So you can try it out if the parameter is specified in memory.


I tried to set the parameter to the value already set and it worked



SQL> alter system set log_archive_dest_1=
  2  'location=USE_DB_RECOVERY_FILE_DEST, valid_for=(ALL_LOGFILES,ALL_ROLES)'
  3  scope=both;

System altered.

SQL> 


If you change the destination for the archives and there are still archives in the old destination then the database knows this an therefore RMAN knows this and will not forget them but backup them when you do your next archive log backup.