add text into ascii file

[luisete2106]

Hello

I would like to add some text into a file, but I don't know how to do.
The text file is this one:

000000001 LDR   L ^^^^^nam^^2200145Ia^45e0
000000001 008   L 090226s9999^^^^xx^^^^^^^^^^^^000^0^und^d
000000001 260   L $$c2007
000000001 269   L $$a01/04/2007
000000001 999	L $$a01/04/2007$$b35978$$cBoletin ICE
000000001 FMT   L BK
000000002 LDR   L ^^^^^nam^^2200157Ia^45e0
000000002 008   L 090226s9999^^^^xx^^^^^^^^^^^^000^0^und^d
000000002 260   L $$c2007
000000002 269   L $$a01/04/2007
000000002 999	L $$a01/04/2007$$b35980$$cBoletin ICE
000000002 FMT   L BK

As you see, this is a list of bibliographics items, the way to identify them is via the LDR filed...So I would like to add this: $$eGEN at the end of the line with the tag 999
as this one for exemple:

000000002 999	L $$a01/04/2007$$b35980$$cBoletin ICE

so the result should be:

000000002 999	L $$a01/04/2007$$b35980$$cBoletin ICE$$eGEN

I think it's possible to do this directly with VI, but I'm not sur.
Thanks to help

Cheers