Derp.

Oh... MrPink is talking about his PC.

There's some mention of clock settings in the comments here (but like I said this is talking about emulators...)

http://vba.ngemu.com/

Do you have a source for the statement?
As far as I'm aware, you cannot change the clock frequency in software, but you can change the so called waitstates for ROM accesses. This basically means that the GBA waits fewer clock cycles for the memory chip to output the requested data. This makes the program run slightly faster but if the memory chip can't cope with it, you'll get invalid data and the thing will crash.

I found a few tutorials on physically changing the gba clock speed (crystal) but also a few emulator posts about setting the clock speed in the bios... could you do the same on hardware?

The answer is probably in here but I'm not a programmer by any means:

http://nocash.emubase.de/gbabios.htm
http://nocash.emubase.de/gbatek.htm#biosfunctions