Retrying a fetch after an error, without restarting the whole loop?

I've been saving picture files that had been stored in a blob field in
an MS-Access database (aka an "OLE Object") to files, and I've bumped
onto some LongReadLen related problems: through trial and error I
finally succeeded in making LongreadLen long enough to reliable extract
all the files. (in Access, the function LEN on such a field reports a
size that's half the number of bytes. Apparently it mistakes it for
Unicode text. I haven't found a better suited function than LEN, though
I haven't searched hard).

Anyway; as this was a process of several minutes, it took some time to
fix the script and start all over.

So I was wondering these two things:

1) What's the best way to temporarily disable RaiseError when I want to
have it enabled for the rest of the script? Say, for one SQL statement?

And 2), in a fetch loop, is it possible to adjust a property like
{ReadLongLen}, and retry the same fetch without restarting the whole
loop? Because this error typically happened several minutes into the
loop.

I think these 2 questions don't mix well. Oh well.

--
Bart.
.