I just returned from New Orleans where a lot of the 1812 reenactors had custom shaped their felt hats. Zinsser's was the choice product for setting the desired shape into hats which are correctly stiff in design. The final stiffness can be adjusted by the amount applied and care used in applying.
Fed
I have found that spraying a very stiff shellacked hat with rubbing alcohol will soften the shellac enough to adjust the shape, it dries quickly if you use the 91 percent stuff, and as alcohol is shellac's solvent, will not lessen it's stiffening ability when it dries.
Just my $.02 worth...
How much of the gallon did the 2 applications consume?