file random write access from within a database

I wonder if it is possible to write to a file from within a database at the chosen position.

What I want to achieve is to modify a kind of header of simple text file (few tens of MB in size).
I could read it to a LOB/table/buffer/whatever, modify few bytes and write it back to the file in its entirety. But this is rather unacceptable solution - I would rather imagine I open a file, set a position, write few bytes at this position (adding or eventually replacing some bytes on specified length), close a file.

I tried fseek, but it works in the Read-like mode only, as I get ERROR at line 1:

ORA-29283: invalid file operation
ORA-06512: at "SYS.UTL_FILE", line 1219
ORA-06512: at "REMS.WRITE_AT", line 16
ORA-06512: at line 1

Regards
Remigiusz

-- 
Pole nakazi

----------------------------------------------------------------------
Remigiusz Sokolowski <remigiusz.sokolowski_at_nordea.com>
pos   : DBA at DIiUSI
addr  : Nordea Bank Polska SA, Luzycka 6A Street, 81-537 Gdynia, Poland
phone : +48 58 667 17 43
mobile: +48 602 42 42 77
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