How to change user password in IB Database 5.6 without SYSDBA password

Hello, All !

In IB Database 5.0 API was added some new functions for users
administration: add (isc_add_user),
modify (isc_modify_user)   delete (isc_delete_user).
Good examples of using it are on and and they works, but i need
_don't know_ SYSDBA Password in run time. I'll try to exclude the bit masks
sec_dba_user_name_spec  and sec_dba_password_spec from
user_sec_data1.sec_flags, but, independently, if SYSDBA Password set then
all works OK (local and via TCP/IP); and if not set, then the error code
returns #335544472=$14000098h, which does not exist in IB API Guide.
A kind of example i need is on ,
but where i can find units IBHeader,
IBExternals which is uses?
What can i do now, may be write into ISC4.gdb directly, using function
May be, the another way exists?
With best regards