No, clear cellulose varnish and shellac are not the same thing.

Shellac is a natural, organic resin that comes from an insect, Laccifera lacca, that is about the size of an apple seed. This bug alights on certain trees indigenous to India and Thailand and during its reproductive cycle feeds on the sap that it sucks from the twigs of these trees. The bug secretes an amber colored resinous substance that is called "lac", a word that comes from the Sanskrit "lakh" which means one-hundred thousand. The resin forms a cocoon around the insect which serves to incubate the eggs she lays. This cocoon is the raw material for shellac and is called "sticklac", because it contains resin, parts of the twig and bug remains. The sticklac is washed and then refined either chemically or by hand, to produce the raw material available for sale to commerce. (Source http://www.antiquerestorers.com/Article … hellac.htm)
This was the origin of the name 'lacquer'.
It is normally dissolved in turpentine to use as a varnish.

Cellulose is a carbohydrate forming the skeleton of most plant structures and plant cells. We generally know it as the source of dietary fiber.

Nitrocellulose is a resin obtained from the nitration of cotton and other cellulosic materials.  This is a chemical process with cellulose and nitric acid as the main ingredients. 

In 1862 the first man-made plastic, nitrocellulose, (branded Parkesine) was created by Alexander Parkes from cellulose treated with nitric acid and a solvent. In 1868, American inventor John Wesley Hyatt developed a plastic material he named Celluloid, improving on Parkes' invention by plasticizing the nitrocellulose with camphor so that it could be processed into finished form and used as a photographic film. Celluloid was used by Kodak, and other suppliers, from the late 1880s as a film base in photography, X-ray films, and motion picture films, and was known as nitrate film. After numerous fires caused by unstable nitrate films, "safety film" (cellulose acetate film) started to be used from the 1930s in the case of X-ray stock and from 1948 for motion picture film.  Partially nitrated cellulose has found uses as a plastic film and in inks and wood coatings.

The main problem is that the solvents used in turning nitrocellulose into a varnish are normally highly inflammable, though the danger passes once they are dry.  There is always a warning on the tin!

In the US cellulose varnish was sold as "Brushing Lacquer".  I had used it long ago when finishing furniture. It seemed to disappear from the market for awhile, but Minwax now produces it. The newer version is not as thick as the older brands.  I did find it useful as a finish for papier-mache bangle bracelets which were covered with decorative papers. Three or 4 coats were needed, but it penetrated the paper to the extent that the final product was nearly plasticized. You could drop them without damage. The lacquer finish also felt nicer to the touch & did not soften when worn, as shellack does. The acetone fumes were the biggest drawback.

Similar products are used when making  fishing lures, such as flies. Also used in model-building as a hardener for fabric and balsa wood;  the old-timers refer to it as "dope."

Yes, stick with shellack for the molds!