Can i change the temporary tablespace for schemas during the transactions??

Question

In My Prod database some of the tablespaces assigned system as Temporary tablespace. I want to change the temporary tablespace for these schemas and the default temporary tablespace of the database.
Can I make this change while the users are accessing the database. Is there any impact If i make this change while the transactions are running.
Below is the change i want to do........
1. Change the users for SYSTEM to TEMP in the temporary tablespace by executing the following SQL
statements:
alter user SYSTEM temporary tablespace TEMP;
alter user SYS temporary tablespace TEMP;
alter user AD_MONITOR temporary tablespace TEMP;
alter use SI_INFORMTN_SCHEMA temporary tablespace TEMP;
alter user EM_MONITOR temporary tablespace TEMP;
alter user ORDPLUGINS temporary tablespace TEMP;
alter user TSMSYS temporary tablespace TEMP;
alter user XDB     temporary tablespace TEMP;
alter user SCOTT temporary tablespace TEMP;
alter user DBSNMP temporary tablespace TEMP;
alter user DIP     temporary tablespace TEMP;
alter user OUTLN temporary tablespace TEMP;
alter user ANONYMOUS temporary tablespace TEMP;
alter user ORDSYS temporary tablespace TEMP;
alter user MDDATA temporary tablespace TEMP;
2. Set the default temporary tablespace to TEMP by executing the following SQL statement:
alter DATABASE default temporary tablespace TEMP;

Answer 1

user11829256 wrote:
But if one transaction is using the old temporary tablespace and if i change the temporary tablespace of user will that transactions of that user fails which is using the old temp segment....It will continue to use the old one till the end of transaction.
Here a quick test (hopefully readable) :
-- session 1 as a dba user
SQL> grant create session to nga identified by nga;
Grant succeeded.
SQL> alter user nga temporary tablespace tmp;
User altered.
SQL> select temporary_tablespace from dba_users where username='NGA';
TEMPORARY_TABLESPACE
TMP
-- session 2 as NGA
SQL> insert into gtt
  2  select * from (select * from all_objects union all select * from all_objects union all select * from all_objects);
80559 rows created.
-- session 1 as a dba user
SQL> select tablespace from v$tempseg_usage where username='NGA';
TABLESPACE
TMP
SQL> alter user nga temporary tablespace pstemp;
User altered.
SQL> select tablespace from v$tempseg_usage where username='NGA';
TABLESPACE
TMP
SQL> select temporary_tablespace from dba_users where username='NGA';
TEMPORARY_TABLESPACE
PSTEMP
-- session 2 as NGA
80559 rows created.
SQL> roll;
Rollback complete.
-- session 1 as a dba user
SQL> select tablespace from v$tempseg_usage where username='NGA';
no rows selected
-- session 2 as NGA
SQL> insert into gtt
  2  select * from (select * from all_objects union all select * from all_objects union all select * from all_objects);
80559 rows created.
-- session 1 as a dba user
SQL> select tablespace from v$tempseg_usage where username='NGA';
TABLESPACE
PSTEMPNicolas.