You can sub in a ceramic of the same value (ceramic would work better actually) but not a necessarily electrolytic (it depends on what the cap's job is). Subbing higher values also depends on what the cap's job is...usually you can get away with it if the cap is a decoupling or bypass cap...but not if the cap is supposed to decouple high frequencies and you substitute a cap in that is much larger (which can't handle high frequencies due to higher parasitics).
Generally yes but there are some circuits that may not like the low Rs of the ceramic capacitor. Some regulators become unstable if the output cap does not have some series resistance.