на Pas-е:
================
type
NewType = <.........>
var
f: file;
HdrSize,Offs: word;
SomeNew: NewType;
const
Something: NewType = <.........>

Этот фрагмент меняет Something:
----------
assign(f,paramstr(0));
reset(f,1);seek(f,8);
blockread(f,HdrSize,2);
Offs:= Ofs(Something)+longint((Seg(Something)-PrefixSeg-
$10+HdrSize))*16;
seek(f,Offs);
blockwrite(f,SomeNew,sizeof(NewType));
close(f);
----------