The past is the past and can't be changed.

Of course, not. :)

You can deal with it, but not change it.

You can change how you think of the past and certain events in it. Has it ever happened to you that you thought differently about one and the same happening?

When I was 16 I started to work at a photography store.
I was quite fond of my boss at the time, but if you had asked me, in my mid-twenties, if I had ever thought of him or associated him with some very important things I had learned, I would probably have looked rather incomprehensible. In my mid-thirties I began to wonder how he was doing and to establish connections between my individual stations and people in life. In this way, looking back at this particular person enabled me to make a different assessment of our time together. I think differently today than I did twenty years ago and also different again thirty years ago. Moreover, the memory of the past is not very different from a mental construction and evaluation of what happened. From the point of view of every age, the thoughts about certain situations change a lot. Whatever you think about your past at the moment always has the greatest meaning. The me of that time was completely different from the me of today.

I am not talking though about things engraved and unconscious emotions and reminders which formed this or that habit wich I am even not aware I do have them.

Do you have an example where you assessed something differently during the course of your life? Sometimes even so that first you thought how bad everything was, then you thought it was not so bad until you thought it was not bad at all?