I believe you can change the "past". I think one day it may be easy to display this to people. I think most of time- "past", "present" and "future", is accessible at the same "time" and that an event of either that takes place in a certain "space" is accessible at that space, whether that event occurred in the "past" or will occur in the "future".
Past, present and future, IMO are just concepts of unreal and erroneous ways of perceiving time, perceptions bred and reinforced into most people from birth on. Regardless, it seems that the complicated human brain can notice that this perception, though perhaps pertinent and important to survival in lesser aware societies, isn't quite correct in terms of what is happening on the planet temporally and nature-wise.
The human brain has been around for millions of years, through many experiences and cultures, those embracing of the true temporal reality, and those not. I believe that the human brain understands, exists and is truly catered towards the natural temporal reality (as well as other natural realities), that has always existed, and that it also contains knowledge past down through human generations, enough knowledge to clue us in and give most people, even those most dismissive of their higher mind's constant nagging and urging (via dreams, gut feelings, the paranormal), the sense that the 9-5 M-F concept of time is way off.
It takes rigid programming to even get people to try to adhere to the concept of past, present and future, and I believe it is mostly language where this is most reinforced, and many peoples have thought "necessary". But you will find that in certain native languages, the idea of past (that something "did happen" or "was yours") does not really exist. (according the their concept of reality that thing "is still happening" - many time these cultures are very memory oriented and past down their history verbally) and in many cases verbs are not temporally specific (though I've only found rare cases where this is the same for the idea of the future, outside of the concept of someone "being someone", i.e. they plan to be someone in the future, hence they are that person now, and always was in the past, and always will be.