login as sys
create pfile='your_init_file_with_complete_path' from spfile;

it should..
I use this always....
and
i do the changes to initsid.ora 
mount and open the database with this initsid.ora
check...if everything is ok.
if so,
then create the spfile from this initsid.ora
and use spfile...as usual....
else i still have my spfile with my original settings

----------------------------------------------------------------------

sys@mutation_mutation > create pfile='mypfile.ora' from spfile;

File created.

-- this will fail
-- bring down the database and start using initsid.ora

sys@mutation_mutation > create spfile from pfile='mypfile.ora';
create spfile from pfile='mypfile.ora'
*
ERROR at line 1:
ORA-32002: cannot create SPFILE already being used by the instance

sys@mutation_mutation > !ls -lt spfilemutation*
-rw-r-----   1 oracle   dba         2560 Apr 25 14:59 spfilemutation.ora

sys@mutation_mutation > !rm spfilemutation.ora

sys@mutation_mutation > shutdown
Database closed.
Database dismounted.
ORACLE instance shut down.
sys@mutation_mutation > startup pfile='mypfile.ora';
ORACLE instance started.

Total System Global Area  202867632 bytes
Fixed Size                   730032 bytes
Variable Size             167772160 bytes
Database Buffers           33554432 bytes
Redo Buffers                 811008 bytes
Database mounted.
Database opened.
sys@mutation_mutation > create spfile from pfile='mypfile.ora';

File created.

sys@mutation_mutation > !ls -lt spfile*
-rw-r-----   1 oracle   dba         2560 Jul  2 22:03 spfilemutation.ora

sys@mutation_mutation >