If you have full edit privileges, anything that's a clear improvement is fine, even if it's small. Please feel free to fix small errors, especially in newer posts or prominent old ones.
But one thing to be cautious about: make sure you try to fix everything there is to be fixed. It's unfortunately common to see edits that fix a glaring mistake in the title ...
I say "no". It doesn't seem like an appropriate edit, because of the new content. What you say about the edit changes the meaning of the answer and does not respect the original editor.
Can you add a new comment to the answer, attributed to anonymous or some low level user, with the new contents in the edit?
I don't think I can actually see the rejection reasons used for your edits, but I strongly suspect that most of yours were rejected as too minor.
The description basically explains it:
This edit is too minor; suggested edits should be substantive improvements addressing multiple issues in the post.
It's not that we don't like to see ...
I rejected this edit as an invalid edit. Please note the reason text:
This edit is incorrect or an attempt to reply to or comment on the existing post.
That's exactly what this edit was - a reply to or comment on the answer.
Adding one's own comments/replies is an abuse of the editing system. If Anon has new information then he/she can and should submit ...
Edit the existing one to be right, or as right as you can make it.
This expectation is built right into the system: editing an answer (a) bumps the question to the front page, and (b) allows previously-locked-in votes to be undone. So if anybody is unhappy with the revised answer, they can flip their previous votes.
Of course, if it's totally unsalvageable ...
If it conflicts with the original authors intent, such an edit should not be accepted.
That being said, I wrote the edit thinking it accurately reflected what the author had intended but had difficultly communicating technically.
The word hydroscopically was used when the word he probably meant was hydrophilic. These words are very similar. He ...
I'm under the impression that any and all edits for spelling, format, and style are accepted and encouraged (with the exception of swapping between acceptable UK-US variants). You're likely seeing some combination of people hunting for their editing badges or just being a little particular.
Initial thought is: Leave it - if you don't know what to do, can't speak to the veracity of the edit, or aren't comfortable with your decision, leave it for someone else. Edits don't wait around for approval long, someone else will deal with it.
Moderators have the same reasons for editing a post that other users have. The block that users without the privilege of editing any post see reports the following points:
fix grammatical or spelling errors
clarify meaning without changing it
correct minor mistakes
add related resources or links
If the edit is done following those points, the edit is ...