I remember the times when our school got our first computers: three C64 with C1541 and one printer. The math teacher who wanted to learn computer science to one day teach it vs. us three who were fluent in assembler, knew the key routines of the OS by heart, and even knew the hardware inside out.
I exchanged the C64's OS ROMS for EEPROMs with four different OS images and hid the switches inside the extension slot. Yes, for this I opened the computers, de-soldered parts, soldered other parts in, etc. The teacher never noticed. Spare keys are fun. Modern school IT would probably faint if a student tried this.
Occasionally, I exchanged the EEPROMs for other variants, like one day where I had an image where the printer suddenly printed everything in reverse. OK, I did not turn around the letters (no space in the code for that, and the printer only had eight user-definable characters, so this would have been a major operation).
The teacher was confused, he just wanted to print a small basic program he had written, and it produced something like "olleH" tnirp 01 instead of 10 print "Hello" (not the actual program he had written). Switching the computer off and on did not help, either. So he asked for help, and I took his C64, turned it upside down, knocked on the bottom three times, and placed it back on the table. During this last motion, I knocked back the switch for the EEPROM selector to the standard ROM image. And then I made the teacher print his text again...