Not more than or no more than /or doesn't matter?

I’ve reviewed the posts discussing the meaning and usage of the phrases, Anything but, nothing less/more than etc. and it helped me a lot. Thanks, first.

My question is about the difference between not more than and no more than.
I fully understand when you use no more than, yet I’m still confused with not (or not ~) more than; some say ‘not’ in not more than makes the whole sentence negative.

For example, the sentence, ‘she is not more beautiful than her sister’, includes the meaning ‘she is beautiful than her sister’ plus NOT. So, they say it means ‘she is not as beautiful as her sister’. Do you agree?

I’m not sure because I sometimes come upon the sentences including not more than just to emphasize its(adjective) negative meaning.

For example, the sentence, Bypass roads are not more innocent than walls, can be written or should be written as ‘Bypass roads are no more innocent than walls’ when you emphasize bypass roads are as bad as walls, I think. (The background information is as followings; The construction of various Israeli bypass roads has contributed in slicing and strangulating Bethlehem district. – Please don’t get me wrong. I’m not trying to evoke an argument on politics. It just happens to be a part of that article. --;)

Anyways, is it safe to think native speakers use both not more than and no more than without any definite rules of usage? If any, would you explain? Thanks in advance.

p.s. I’ve tried to register, but somehow I couldn’t see any message on the screen that I’ve been accepted as a member. Shall I just wait or try again?