Yes you can change at will
SQL> conn / as sysdba
Connected.
SQL> alter database force logging;
Database altered.
SQL> alter database no force logging;
Database altered.
SQL>
Just don't forget that force logging is probably there for a reason (eg standy) so you need to make sure you don't break any managed recovery rules you have in place.
Even *with* logging, APPEND for large data loads is more efficient than without