You CAN do that - but you don't have to.
The double overhand grip is advisable, in general, for those that need a built-in regulator for the volume work, have some kind of injury problem that prevents them from doing an alternate grip or whatever odd reason I haven't thought of.
If it fits it for you, be my guest. The progress made on that program, both in strength/size/conditioning has absolutely floored me. Keep in mind that I'm VERY adamant about TM, form as well as addressing that other areas of training are addressed. It's certainly not for everyone but it's the only program, as of now, that i have any interest in coaching personally.