On nethserver page should have a tab for viewing the files and as well as be able to edit the files and apply.
Could you please formulate again your question, I did not understand
I would like to edit the files through http and make corrections and apply. Developers should create this condition.I just came from pfSense and it has this option, instead I use putty.
Which kind of files?You don't need/have to edit manually configuration files on NS
operating system files, squid.conf and other
Read the manual
Files are created by a template system which regenerate them from events. So your changes will be erased and go back to original versions. You have to do custom-templates