I have just created a new multiplexer/demux symbol, the NX3L4051 (merge, datasheet). This IC could be used as mux or demux.
The current symbol is working as mux if we want input on the left of the symbol.
For design where it is used as demux the symetry broke this rules since selection of address and enable are on the right of the symbol.
How could we solve this issues, 
?
Should we split the part in two? use an alternative symbol (DeMorgan) as recommended here?
Any suggestion would help.
For me your symbol looks like it would switch all inputs at the same time.
You could have made an alternate symbol in far less than the time it took you to agonize and write about it.
Dear Piotr,
Here is an example where on the right I want to use it as a demux
Using the “Mirror” or “Rotate” functions in the Schematic Editor saves worrying about an alternate symbol.
@jmk , It is what I want to avoid, since mirror changes all pins. In the case of alternate parts I could keept the command on the left of the symbols:
That wasn’t mentioned above.
Only one symbol is still needed, as, for a single job, edit the symbol by block mirroring only the control part or the switching part.
For a permanent library part, do the same but save the edits in a personal library as two symbols. The MUX and the DeMUX. Either way, the modification is an under 30 second job.
Here’s an FAQ on the subject:
@ML9104 , thank you for your answer. My MR was rejected for the reasons mentioned.
I will use local library to solve this issue.
That’s the best way.
It was actually, you have to read behind the sentence:
And the figure in post 4 showed what OP had in mind.
A solution that’s too clever for its own good would be 2 units stacked on top of each other, which can be mirrored independently. But I think the solution of two symbols, either as variants or separate symbols is simple and best.
Nahhh,
Not even 30 seconds. Just as quick as swapping a couple of gates in a package.
@penoud My apologies for this:
I overlooked your comment.
Except the next time you refresh the symbol from the library you will get the old one. Really the difference boils down to whether you save the symbol in a private library or you modify it every time you start a new schematic.
Correct, but you may want the old one next time. You may be MUXing instead of DUXing. It is the same symbol, the mirroring is only to improve the readability of the schematic. Maybe next time you will want the control pins on the right instead of the left for the schematic aesthetics.
Basically, there are four versions. Is it worth the effort to open the library and choose which of the four you require, or just have one and spend under 30 seconds changing to suit the schematic layout?
I know, the Jury is out on this one. Personal preferences reign, except in the official Kicad libraries, of course. 
No, only two. You can get the other two by mirroring the whole symbol. And if you want the signal to flow the other way.
One can be named in the library as blah-blah-MUX, and the other blah-blah-DEMUX. No need for blah-blah-SUX. 
Except; you also may desire to change footprints which means different symbol pin outs. There is the NX3L4051HR and the NX3L4051PW. This means four mirrorable, not memorable, symbols. This really does SUX.
If I could afford that many parts I’d spend the money on something more enjoyable. Good night!
Or create a two-unit symbol, one unit for S etc. and one for Y.
To close this subject,
I want to thank you all for your help.
There are many reasons to prefer one solution over another. The rules are the rules, and in the end, I accept it. Yes, my nice idea was rejected for addition to the library, but that’s part of the game. The libraries are great, and I can cope with having a MR rejected from time to time, especially since I didn’t follow the KLC that I should know by heart.
