As hopefully a compliment to that last statement..
Over the years and years ago I have had exposure to and perfomed meditations from other beliefs.
Most memorable to me was one of the Taoist variety. I forget all the specifics of it, it was quite involved, as can be certain Tibetan Buddhist meditations.
But the tone of it was differing. At the closeur or end, one had to be very careful to end the meditation and meditational state with a definitive form of closeur. So one would not remain in a meditative state and thusly be subject to harm by spirits or others.
Whereas in a tibetan buddhist meditation the end or closeur is always invariably followed with a dedication of any merit garnished by the meditational practice to others. And perhaps at some level the continuance of a meditative state is rather encouraged.
the taosist variety I could see could be thought of leading to a thought of real place, exclusion of others, that way of thinking, would be a exclusive meditation. Shaministic meditations seem to lead that way as well in their nature.
The buddhist meditation due to compliment of dedication of merit and perhaps continuance of state, would be a inclusive meditation.
So I would suggest for one to enter a formless realm considering the perameters of buddhist meditations, would be almost impossible if those are done in the customary fashion. One would have to deviate not only with intention but with actual practice.
Other mediations of the mundane fashion..to my opinion would lead directly there.
UNfortunately for those deluded ones so practicing if they continue in that fashion.
Such peoples would exhibit great powers of cognition and such things as mind reading and forecasting, and then mistakeingly think, while in this realm but headed to another...well it is sure I am enlightened. They are not. As H points out even the formless realm eventually ends.
"This order considers that progress can be achieved more rapidly during a single month of self-transformation through terrifying conditions in rough terrain and in "the abode of harmful forces" than through meditating for a period of three years in towns and monasteries"....Takpo Tashi Namgyal.