Stencil printing flux is easy if you know what to expect before attempting it. It is easier than stencil printing solder paste in most common aperture ratio (.66) situations, although both large (>1.0) and small (<.4 area ratio apertures suffer from printing defects when stenciling flux.>
When designing a stencil for your application, keep in mind all fluxes will slump – there are no solder particles holding the brick-shaped initial deposit together. Keep your stencil thinner than you would for a paste application, flux is generally over-applied. Also, airlessly packaged fluxes act differently than standard fluxes, so make sure you are using a flux that is appropriate for your application.