I know that changing the order and/or the form of words in an idiom or a saying is wrong, but I am just asking to know more and get updated advice.
We have “kill two birds with one stone”, but the other day I used it in this way: “ Why not killing two birds with one stone”, later I changed it to the original form and wrote this: “ why not kill two birds with one stone”.
So, I just want to know, isn’t it possible and/or common if we change the wording of an idiom, proverb and saying even a little so that the meaning is not lost?
It depends on the phrase. Some of them are practically invariant, and some of them accommodate considerably more modification. For example, the idiom “kick the bucket” can’t be modified at all, except for inflecting the verb; you could say “kicks the bucket” or “kicked the bucket”, but not “the bucket was kicked” or “kick the blue bucket” or “kick a bucket” or “kick the buckets”. “Kill two birds with one stone” is similar; inflecting the verb as you’ve done is fine, though other modifications will make the idiom lose its meaning. However, I must add that without further context “why not killing two birds with one stone” sounds a bit strange; what did you say/write before and after this, or what statement were you responding to?
“ Why not killing two birds with one stone” is bad grammar. The sentence doesn’t have a verb. “Killing” without an auxiliary verb (is, was, will be) is a participle or gerund. You wouldn’t say “I killing them.” You would say “I am killing them.”
“ Why not kill two birds with one stone?” is a perfectly good expression that anybody would use. For example, I might say “You can help a charity and get a tax deduction, so why not kill two birds with one stone?”
Sentences in English don’t need explicit verbs. “Why not the one on the left?” is a perfectly valid sentence in English and all speakers will understand the implied verb (and subject, in this case) with sufficient context (for example, if it’s a response to the statement, “I like all the ferrets, except for the one on the left.”) It’s not hard to think of similar “Why not …?” sentences that take a gerund complement. But it’s hard to think of a semantically plausible context for which “Why not killing two birds with one stone?” would be an appropriate response, hence my question to the OP. At any rate, it’s not even clear from the OP whether the utterance was meant to be a single sentence or whether it was just some sequence of words which appeared somewhere in a sentence.
According to whom? People change idioms constantly, and they change over time. Some change to the point where they make no sense (e.g., “I could care less” instead of “I couldn’t care less”), which is annoying, but if the meaning isn’t affected, there certainly isn’t anything wrong with changing it to fit the situation.
If a friend in the explosives industry looked tired, for example, I’d probably say he looked like he was burning the fuse at both ends. It still retains the original sense of “burning the candle at both ends,” and people would understand what it meant, but it would be a more personal and appropriate use of the idiom.
Well, often the vocabulary in these phrases is set, so you can’t say “terminate the lives of two avian creatures using the instrumentality of a single instance of a rock” without it sounding silly and possibly confusing people.