adob.stream - altering a byte() result

Hello all,

I've used adob.stream to get a byte() array of data.  Using midb() to read 
every byte/character from that array works ("data(i)" doesn't :-( ).

The problem is that I can't seem to find a method to *alter* the byte() 
string/array. using "midb(...) = ..." thows an error, and tryng to split it 
(using leftb() and rightb() ) and glue something between the parts causes 
the result to become a string (checked using typename).

... and I just found out that "leftb()" itself returns a string, and not 
just a small byte() array.

Some googeling returns a number of examples to *display* the contents of a 
byte() array, but I can't seem to find any example altering it.

Does someone know how its supposed to be done ?

Regards,
Rudy Wieser