Fonts are possible to transfer. Basically you create a new font in the new sprite collection, and use the other font data objects instead of creating a new one. That should work fine.
Sprites on the other hand are more complicated. Not impossible, but depends very much on what you're trying to change. If its just stuff in a scene, its perfectly doable - you need a script to catalog all sprites and the names, and then a script to restore the appropriate data later from a list of sprite collections. Its really hard to do this in a totally generic way which will work with any number of prefabs, asset bundles, etc. but if your needs are a bit constrained it should be doable.