The first thing I'd do to make that more maintainable is refactor it all into a series of well-named minimized-coupling subroutines, no longer than 20-30 lines each, and ideally about 10 lines each. That'd also remove about 90% of the global variables, which are generally also a sign of fragile code.

The second thing I'd do is take that middle switch out of there, and capture the regularities with code, and the irregularites with data. I bet you wrote a lot of it with cut and paste, and that should always be a clue.

Let me repeat. Cut and paste is generally a clue that you're doing something wrong.

On a longer-term basis, factoring out some of that code for re-use might be useful, which would also make testing easier. But unless you're also doing some similar tasks later, that might be an expense with no payback.