文件读写(20分)

要把一个文件（无类型）的读出来，然后写入该怎么做啊？AssignFile(yf, filed); //??????????
procedure Tyazhenmdtj.LMDButton21Click(Sender: TObject);
var
s:string;
reg:tregistry;
i:integer;
a0,a1,a2,a3,a4,a5,a6,a7: string;
ff,yf:file;
bs:byte;
filed:string;
hangshu,dread:integer;
getyz:array[1..800000] of byte;

begin
Reset(yf,1);
BlockRead(yf, getyz,filesize(yf), dRead);
hangshu:=(filesize(yf)-32) div 24;

i:=1;
while (i<= hangshu) do
begin
getyz[32+(i-1)*24+15]:=strtoint(stringgrid1.cells[1,1]);
getyz[32+(i-1)*24+16]:=strtoint(stringgrid1.cells[1,3]);
getyz[32+(i-1)*24+17]:=strtoint(stringgrid1.cells[1,5]);
getyz[32+(i-1)*24+18]:=strtoint(stringgrid1.cells[1,7]);
i:=i+2;
end;
i:=2 ;
while (i<=hangshu) do
begin
getyz[32+(i-1)*24+15]:=strtoint(stringgrid1.cells[1,0]);
getyz[32+(i-1)*24+16]:=strtoint(stringgrid1.cells[1,2]);
getyz[32+(i-1)*24+17]:=strtoint(stringgrid1.cells[1,4]);
getyz[32+(i-1)*24+18]:=strtoint(stringgrid1.cells[1,6]);
i:=i+2;
end;
closefile(yf);
AssignFile(ff,filed);
Rewrite(ff,1);
for i:=1 to filesize(ff) do
begin
write(ff,getyz[1]);
end;
为什么不行呢？提示是类型不匹配
[Error] Unit2.pas(309): Incompatible types: 'procedure, untyped pointer or untyped parameter' and 'Byte'
如果用blockwrite的话，提示i/o error 103，即文件没有打开，不知道是什么原因啊。
高手帮忙指点一下。对了，如果把文件读出来修改几个数据后重新写入，一般该怎么做啊？
能不能写入到指定的位置呢？

procedure copy_file(fss,fdd:string);
var fi,fo:file;
buff:array[1..128,1..10] of byte;
numread,numwrite:integer;
begin
assignfile(fi,fss);
reset(fi,1);
assignfile(fo,fdd);
rewrite(fo,1);

repeat
blockread(fi,buff,sizeof(buff),numread);
//在这里你可以修改BUFF内容
blockwrite(fo,buff,numread,numwrite);
until (numread=0) or (numread<>numwrite);
closefile(fi);
closefile(fo);
end;