Jim:
This is OK for old fashioned temporary tablespaces with datafiles.
Iyyappan has the true temporary tablespace and switching permanent/temporary fails with it:

system@oracle>system@oracle> create temporary tablespace temp1
2 tempfile 'g:\orant\database\temp1a.dbf' size 1M reuse
3 extent management local uniform size 64k
4 /

Tablespace created.

system@oracle> alter tablespace temp1
2 default storage (pctincrease 1)
3 /
alter tablespace temp1
*
ERROR at line 1:
ORA-03217: invalid option for alter of TEMPORARY TABLESPACE


system@oracle> alter tablespace temp1 permanent
2 /
alter tablespace temp1 permanent
*
ERROR at line 1:
ORA-03217: invalid option for alter of TEMPORARY TABLESPACE

system@oracle> alter tablespace temp1
2 add tempfile 'g:\orant\database\temp1b.dbf' size 1M reuse
3 /

Tablespace altered.

system@oracle> alter database tempfile 'g:\orant\database\temp1a.dbf' offline
2 /

Database altered.

system@oracle> alter database tempfile 'g:\orant\database\temp1a.dbf' drop
2 /

Database altered.