Not sure if there's a more appropriate subboard for this, but, well, I was having difficulties practicing midboss Marisa's second non, so I hacked my .dat so that you only fight her nonspells when you select stage 4 in stage practice. And it turned out it was pretty easy to hack the stage files for the other stages too, so I've done 4a, 4b, 5, 6a, 6b, and extra. You can download it here:
https://dl.dropboxusercontent.com/u/11812361/th08_nonspell_practice.datNotes:
To use, just replace th08.dat with this file. Make sure you save your old .dat though!
I don't think there are hard nons on stages 1-3, so I haven't included those. Those stages should play normally.
The stages listed above should basically skip to the boss portions right away, kill all the spells really fast, and let you fight the nonspells. This should happen in full runs, stage practice, or even the demo.
On stage 5, however, I couldn't get Tewi to stick around, so it jumps straight to Reisen. Sorry! Uh, if you're having trouble with Tewi, maybe cross-train (haha get it) on another game for a bit.
On the extra stage, you'll be at super low power the whole time, but I don't think this is too much of an issue, just more time to practice, right? I don't intend to fix this whether you agree with me or not though.
I tested these all on Lunatic except 6a (which I... haven't unlocked on Lunatic somehow), so bug reports are welcomed and encouraged.