Nope, you can't do that. That would require magic. The 64 user-progammable programs are a group of effects parameters -- reverb type, delay time, number of delays, feedback, etc. That is, you can set up an effect that has all the settings on it tweaked to your liking, save it, and have it available in the future just by loading that program. But it is
not a MIDI sound module and has nothing in it to respond to MIDI note messages.
A MIDI adapter pickup for the guitar would also do you no good without the hardware to take the signals from the pickup and convert them to MIDI messages. Something like
the Roland GR-33 would be required.
It sounds like you are confusing effects with instruments. Effects are just processes that get applied to an instrument signal that alter it in some desirable way -- adding distortion, or delays or chorusing to thicken the sound, that sort of thing. Whether the effects processor is analog or digital is not really relevant to the thing you seem to want to do. A MIDI synthesizer has
sounds -- created electronically in some fashion like manipulating basic pitched waveforms. These sounds can be further manipulated by passing them through effects just like a guitar's sound is, but the sounds themselves are not effects.
So there is nothing you can do with MIDI between the keyboard and the effects box except to send it MIDI messages it can respond to -- things like changing the patch from #29 to #47, or changing the chorus depth parameter, or something like that. In other words, you can use MIDI to
automate the effects processing.
Does that make any sense?
If you don't like the sound of the Roland effects box, well, maybe there's another that you would like better. Or maybe yu justyt need to explore the various parameters that you can change on the box and find better sounds. Are you simply picking the pre-programmed effects patches? All the effects should have several things that you can adjust. Play around with them.
Another thing is, don't expect a box with "all the best guitar sounds at my fingertips" to be a substitute for being able to play. No matter how good the guitar is or the amp and effects chain, if you cannot play very well it will sound like you cannot play very well. No magic there either, just practice practice practice.