So many thanks!
Selecting images instead of folder works like a charm - great! Mirror options work great, but:
1. The most important feature - lock aspect ratio - is not well coded. Sorry, this is my fault - I should give you more explanation. So here it is: it is not about having same values in the input LUA panel, but the same values in the final UV transform for S.X and S.Y. - see the screenshot. So please add aspect ratio option to the input panel, and if a user chooses aspect ratio as 1 we shall see same values in the final UV transform for S.X and S.Y (with +- signs when the mirror is used). So the code for final S.Y may look like S.Y = c*S.X, where c is aspect ratio.
2. A bug: when I open any group in the node graph and run the script the final node occurs in the scene tab, not in the tab where I am currently in. It works only for updating the script. What I have to do is go to the scene tab, cut the node and paste it into a desired tab.
You are the man! It's almost done