If I remember correctly, Bashar has spoken about quitting smoking by moving yourself consciously to a physical reality where you never smoked in the first place. You might get some ideas from it...

https://www.youtube.com/watch?v=hxMIfXaN1Gs

I tend to think that existing manifesting methods already alter the past because everything happens Now (because only Now exists) and the illusion of past/future just updates automatically to reflect the evolved Now.

See Is it really possible to shift into a parallel reality with a different past?

But what you seem to be asking for is a conscious awareness of the past altering i.e. being aware of multiple simultaneous timelines with one timeline acting as a control variable.

There was an episode of "Star Trek - The Next Generation" called "Yesterday's Enterprise" where the writers explored these kinds of ideas in an entertaining and thought-provoking way...

https://www.youtube.com/watch?v=52KFUdU1jaQ

...the character of Guinan provided the control variable on behalf of the television viewers.

From higher-than-physical levels (e.g. dream states, astral projection etc), these kinds of conscious time-based alterations are no problem at all because time is an illusion of the physical plane and we are not constrained by it when not focused there.

But physical reality was intended to be a single-point-of-focus environment in order to provide the complete immersive illusion so, apart from the odd Mandela Effect glimpse, I'm not sure how you would consistently retain the awareness of the previous pasts that have been altered.

However, over the past few decades, physical reality has become considerably more fluid so possibly it's only a matter of time (excuse the pun) until it's possible to do this. Your ideas might be inspired by an awareness of changes that are coming.

to live in the now would be better for you. if you need to change the past for your future do it in the now. you made some error in the past repent fix what you did wrong first inside then outside. you have free will and can act in the present moment. if you want to change it in your present reality do the work that you need to do for it. it is never to late to do the right thing. why do you waste the present moment? if you desire to make it part of your past use the present moment to make the necessary change. then in the future that is starting now it will have really happen in the past. learn the value of the now the present moment. to only imagine is not enough. you can imagine stuff it does not make it true. test it and try it. and you will see that some things are not quite like you imagine it. you can be missing knowledge about stuff with in or outside of you. good example would be some inventor that add some idea in their imagination the problem is when they try to make it for real and put it in this world it take work and many try to correct what is making it not work as they imagine it. in the processes they learn many important things that using only imagination they would not have know.

good example look at plane. do you think the inventor just imagine it and it started flying on its own? or something smaller a light bulb. do you think the light bulb you are using today came only from one man imagination? someone got the idea and tried to make it happen they have perfected it some in their life time for some other they have worked on the same invention each perfecting it until it worked.

Thomas Edison is usually credited with the invention of the light bulb, but the famous American inventor wasn't the only one who contributed to the development of this revolutionary technology. Many notable figures are also remembered for their work with electric batteries, lamps and the creation of the first incandescent bulbs.

In 1800, Italian inventor Alessandro Volta developed the first practical method of generating electricity, the voltaic pile. Made of alternating discs of zinc and copper -- interspersed with layers of cardboards soaked in salt water -- the pile conducted electricity when a copper wire was connected at either end. While actually a predecessor of the modern battery, Volta's glowing copper wire is also considered to be one of the earliest manifestations of incandescent lighting.

William David Coolidge, an American physicist with General Electric, improved the company's method of manufacturing tungsten filaments in 1910. Tungsten, which has the highest melting point of any chemical element, was known by Edison to be an excellent material for light bulb filaments, but the machinery needed to produce super-fine tungsten wire was not available in the late nineteenth century. Tungsten is still the primary material used in incandescent bulb filaments today.

the light bulb you use today it took 110 year to make it work.

http://www.livescience.com/43424-who-invented-the-light-bulb.html

you cannot expect to only imagine something to make it work. at best it is a basic plan that need some work.

the best way to have something in your mind is when you do it. that is what you call experience.

good example you can imagine you are the first man that put the foot on the moon. if you did not actually do it, it will not stay in your mind for long what you have imagine. and if some one ask you information about that experience it can be very different from what it is actually.

Your question raises questions. I recently read a book called The Intention Experiment and there have been experiments where intentions have an affect on past events, as if those events were changed by present intention. Out of an abundance of curiosity, why would you need or want to go back and insert a situation in the past? However, my simple answer to your question is, we are more powerful than we acknowledge and our minds have the power to bend, shape, and warp time. Very few people today can let go of the linear time continuum to even consider your question. The implications of changing the past are huge.