Changing a PAL A1200 to NTSC following those instructions would leave you with a 60Hz PAL output (Hmmm, doesn't that actually exist?).
I think the original poster was thinking of replacing the composite video hardware and RF modulator so they could use an NTSC TV set. Sounds difficult unless you are very good at soldering. Without changing that stuff the RF output is likely useless and the composite output would be monochrome (Actually PAL colour, but the NTSC TV would ignore it).
BTW If you have a PC most TV tuner cards can be set for PAL or NTSC (Mine lists 2 variations of NTSC, about 5 PALs and SECAM). This would let you use your PC monitor as a PAL or NTSC display.
