> When a mirror is continued, does httrack read the options 
> from doit.log?
Yes ; using 'httrack --continue' should work
Note that it is never used by *win*httrack, which rely on 
winhttrack.ini

> When I tried this, the mirror started from the beginning 
> again. I had to also specify the --continue option for it 
> to work. Is this the correct procedure?
Yes ; and the engine should have rescanned, but quickly, 
without downloading data

> Also, doit.log says not to edit. If the command line is 
> read from this file, is it ok to change some of the 
options 
> before continuing a mirror?
Yes :)