Iv'e noticed based on the dictionary that the words "to change" and "to alter" (=alterations and changes) are interchangeable. My distinguishing is correct? Are there cases which they are not interchangeable when we are talking about changes? or maybe for English native speakers one of them is mainly in use in specific area?
According to the Cambridge dictionary, change has six meanings, and alter has only two - and one of them is so rare that I have never heard it used. Only a third of one definition of change (BECOME DIFFERENT) corresponds to the alter meaning.
Within this meaning (to make or become different), both change and alter can in principle be used transitively (something is changed by an external influence) or intransitively (something changes on its own), however alter is almost always used transitively
We've had to alter some of our plans - transitive
Whereas change sounds equally good transitively and intransitively.
We've had to change some of our plans - transitive
The city has changed a lot over the years - intransitive.
change can apply to anything from the tiniest tweak to a complete overhaul or replacement, whereas alter is used only about small changes.
"Changes" is the more general term of the two. You can experience certain "changes in your life", but not "alterations to your life".
The word "alteration" has the connotation of external interference, of an outside agent doing something to bring about modifications. Change is something that can happen on its own.
E. g., you can say,
"I've changed a lot since my college years."
But "I've been altered" would imply that you have been abducted by aliens and they have performed some kind of surgeries or a mental/telepathical intervention, and because of that, your body or mind started functioning and/or reacting in abnormal ways.
So "alter" always has this air of artificialness and external intent about it, while "changes" can be completely natural and accidental. Also, "alter" has connotations of abnormality, which is why an umbrella medical term for mental problems is
Or there can be "alterations of the human gut microbiome".
Another difference between "alter" and "change" in those cases where both can be used is that "altering" implies changing some minor specific things about something, while "change" would be all-encompassing.
"If it were to rain on our wedding day, alterations to our plan were possible..." (source).
This would mean that some parts of the wedding would be modified, but there would be no major changes ("major alterations" sounds a bit odd).
On the other hand,
"There has been a change in plans..."
can mean that the plan has changed completely (e. g., instead of going on vacation to Paris you decide to go to Bali, or to stay home entirely).
"Syn. -- Change, Alter. Change is generic and the stronger term. It may express a loss of identity, or the substitution of one thing in place of another; alter commonly expresses a partial change, or a change in form or details without destroying identity."
from Webster 1913's version