Of course you could probably switch to a different BSP by pressing a switch, but I have a few questions on it.

Would this script work, or what adjustments should I add to it?

(global short bsp_switch 0)

(script startup swap_bsp
   ;; script stuff
   (sleep_until (trigger_volume_1 (players)) 15)
      (if (bsp_switch == 1) then
         (switch_bsp 4)
      )
      (else
         (switch_bsp 3)
      )
   )
)   

I have a feeling that my syntax is completely wrong, especially with the if statement (thinking too much of maxscript >_>). Now, if that script would work, how would I make it so that when I press a switch, the value of the variable bsp_switch changes to a different value?

Help would be appreciated.

Change (bsp_switch == 1) to (= bsp_switch 1). Just one of the things in HSC syntax.

There's also no then command for HSC. What you want is :

(global short bsp_switch 0)

(script startup swap_bsp
;; script stuff
(sleep_until (volume_test_objects trigger_volume_1 (players)) 15)
(if
(= bsp_switch 1)
(begin
(switch_bsp 4)
)
(begin
(switch_bsp 3)
)
)
)
)

Alright, now how would I make so that a control switch (like the bridge control on a30) changes bsp_switch? That's the part I'm absolutely clueless on.