I’m recording analog instruments and am wondering if there is a way to apply a soundfont to change the character of the sound? So, I want to make my plastic melodica sound more like a clarinet. Or even make it sound like a piano! My guess is no, but is this even in the realm of future possibilities, from a DAW?
Soundfonts do not “change” sounds. Soundfonts are a collection of sounds for use with samplers. (SoundFont - Wikipedia)
There are many ways to modify sounds (such as “filtering”), but it is very unlikely that you will be able to modify the sound of a plastic melodica to sound like a clarinet or a piano. If you want to change instruments, the usual way is to use a “MIDI Sequencer” to control a synthesizer or sampler, and then change the patch (instrument) that the synth/sampler is playing. Most full-featured DAWs have a MIDI sequencer built in.
You may find this YouTube video informative: https://www.youtube.com/watch?v=xJaCdGdpRTo