And how is that going to fix your shielding problem? I'm very sure that you're capable of using L to shield when you think about using L to shield.
You said it yourself, it doesn't matter if you can do something by thinking about it, you need to be able to do it while you're focusing on more important matters. So why would you play a level 3 and give yourself time to think about it? You don't have to focus on fighting, because level 3's are morons. I wanted to check just how bad level 3's are, so I went a started a match. 1 v 1, my Falco vs Level 3 Bowser. I didn't move.
Bowser slooooooooooooowly walked across the stage towards me. Halfway across the stage, he jumped backwards. Then shorthopped straight up. Then sheilded, and dropped the shield into a downsmash (still halfway across the stage). He then walked towards me again, proceeded to jump over me three times in a row for no apparent reason, ran back across the stage, ran back towards me, jumped over me one more time for good measure, grabbed me and didn't do anything, then finally walked up to me and jabbed me. The whole ordeal took about ten seconds.
Learning to shield with L in this scenario is useless, since, as you said, once you play a human, that's all going to go out the window and you'll be reverting back to your old ways.
The fact that level 9's don't give you opportunity to practice is a good thing. If you can't do the tech, you should be in training mode learning it. If you can do the tech, you should be learning how to use it while under a crap-ton of pressure. This is how I originally learned the timing for Falco's SHDL. And it was hilariously useless in the match, because the CPU shielded every one of my Lasers. But it doesn't matter, because I was learning how to consistently SHDL while someone was actively pursuing me and trying to stop me.