You could put it in a .bas file, store it in flash, and set it to autorun. There’s an example mentioned on this thread, and @rlauzon used it in his collection of code examples, explained here in this text file.
That will work for most stuff, though there are exceptions. Some of the OPTION commands can’t be put in a .bas file, for instance, like CPUSPEED. Setting the default drive works though.
Also worth mentioning – it might not survive if you flash an updated firmware. That said, I have actually seen it persist across (maybe just minor?) updates to PicoMite. The only time I know I’ve seen it get lost is when I flashed an entirely different firmware (like MicroPython) and then returned to a PicoMite firmware.