You can record samples to the synths and drums without overwriting the presets. The 8 buttons just provide quick access to the last instrument you used with that button. Press SHIFT + (1-8) and the screen will show all the available engines. Scroll to SNAPSHOT and you can see any samples you have made, although they will be titled as numbers like 202007200035. You can rename them if you plug the OP-1 into a computer and change the file name.
SNAPSHOT works the same for drum or synth and you can swap sounds between them. The LIFT and DROP buttons work on anything, so if you press LIFT on some audio on one of the tape tracks and you go to a drum or synth track (or both) and press DROP and it will become a sample in there. Works in reverse too.
If you are working with a sample or an engine setting that you want to save, then just hold down the 1-8 key that you are currently in. The screen will say “Saving” for a second, and then that sample/setting will be available under SNAPSHOT (scroll to the bottom for the most recent one). Once it is saved you can access it through SNAPSHOT with any other 1-8 button. Changing the current sample/engine for a 1-8 button will not delete any other saved samples/engines.
There is a memory limit on the OP-1 and you can back up the files to your computer when it gets full. These will be audio files, but you can drag and drop them between the OP-1 and your computer with your settings saved because there is information stored in the audio file that the OP-1 will read.