You can add solid modifiers that either become part of the model (like for casting sprews for example), or infill modifiers to make areas solid, or even voids in the model etc. Depends on your slicer program. I use Prusa’s fork of open-source project Slic3r. It will work for most printers and should work for your resin or FDM. Even has text capabilities now. Lots of tutorials available. Some pretty cool tricks can be done.
It’s unnecessary with resin printers since the infill is solid. I use Cura and Zortrax slicers for my FDM prints. I’ll take a look and see what options are there.
Does the infill have to be solid on resin printers?
I only have a Form3 from FormLabs. There is no setting for infill. It’s all homogeneous.
I recently got into resin printing and use a 3rd party slicer (Lychee).
Slicer features include the ability to hollow out a solid body with a wall thickness of your choosing- like a chocolate Easter bunny 
. You can also call out a drain hole for internal liquid resin to escape for post processing. Otherwise, all resin printed parts are solid provided your 3D model is solid to start with.
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