Well, someone figured out that all the NEW command did was set a single byte to #400, which was the top of usable memory or something, and then the interpreter would see .. nothing. So we wrote an "OLD" command that simply replaced that value with maximum memory avialable - and voila, program loaded again! I'll never forget the joy of typing in that 10-line OLD command, loading up a protected game, breaking into BASIC, seeing that the game had been 'wiped', then typing 'OLD' to get it all back again .. so I could save it to tape again. That moment sent me off on a wonderful journey that is still not over, 30 years later .. I think copy protection is responsible for motivating more software development by hackers over the decades than, perhaps, any other aspect ..
The Apple II disk drives featured head movement that was operated by programmed I/O. For increments of a stepper motor were required to go from one track to another. This made it possible to write data in quarter track increments, giving rise to one copy protection scheme.
A conventional track-by-track disk copy program would not correctly copy data written in a spiral pattern using quarter track increments.
There were also schemes whereby tracks were written at a different speed. The logic-state-sequencer state machine for shifting bits from the head would still read the data correctly, but the program could tell a copy made at a conventional speed from the genuine article, due to the different size and content of the gap.
Programs that did this sort of thing would tend to have to be cracked by removing all the checks, and replacing their disk loading routines with conventional ones that read ordinary tracks that are copyable with any disk copying utility.
These parameter files were generally created by the community, who raced to be the first to gain fame publishing the keys for whatever just released or impossible-to-crack software came out. For a brief time, there was a thriving underground of parameter file traders.
I knew of someone who'd actually compiled a book of parameters, got it printed at a local copy shop and would sell it for $16 at swap meets. He eventually got a C&D from the makers of Locksmith claiming that the parameters he was publishing were covered under their copyright (even though they were created by the community). Not sure if they actually had a legal case, but he wasn't about to find out.
I used Nibbles Away and Locksmith, but never for disks that needed the parameters; just ordinary "garden variety" copying.
1st stage loader was easy, but when I started the game from the tape copy it just printed:
Much later and after some Jolt Colas I got it running on the copy :-)