I am trying to switch my X360 Arcade from PAL to NTSC to play MGS HD Collection I got as Xmas gift.

I stumbled upon "Enigmah Video Mode Select CD", which as I understand was used back in the days of the original X-Box.

Is is possible to use one such program to switch the regions back and forth between NTSC & PAL ?

I don't have a JTAG'd 360, though the drive is flashed with LT+ 3.0.

Nope, its not possible. Return the game and buy the correct region.