ORA-02096: specified initialization parameter is not modifiable with this option

Though the initialization parameter is modifiable, it cannot be modified using the specified command.

For example, you try to change the memory_target initialization parameter for your session:

SQL> alter session set memory_target=1;
alter session set memory_target=1
*
ERROR at line 1:
ORA-02096: specified initialization parameter is not modifiable with this option

Although you can change the value for memory_target, you cannot do so for your session.
You can check the v$parameter data dictionary view in order to see if a certain parameter can be changed in a session:

SQL> select isses_modifiable, issys_modifiable from v$parameter where name='memory_target';

ISSES ISSYS_MOD
----- ---------
FALSE IMMEDIATE

As you can see, ISSES_MODIFIABLE (Can be modified using alter session command) is set to false, hence this error message.

The enumeration values for issys_modifiable

FALSE : it means that the parameter cannot change its value in the lifetime of the instance; the database needs to be restarted for changes to take effect.

IMMEDATE: value means that it is dynamic and can be set to change the present active instance as well as future database restarts.

DEFERRED: is also dynamic, but changes only affect subsequent sessions, currently active sessions will not be affected and retain the old parameter value