Nope... Your current permissions:
$ getfacl logs
# file: logs
# owner: euser
# group: grpi
say that any new file created after these permissions were applied get 644 plus guser gets 6 (rwx) (and mask is set to 6 -- rwx-- to allow this).. So guser is able to edit those any new file by default, no matter who owns them... However, he does not have effective write permissions in the directory.. So he cannot add or remove (unlink) files in that directory..
Running my commands will do nothing but allow the user "guser" to add or remove files from the directory (mask is not an effective permission) and will not modify your normal 755 permission.
Basically, right now you can have euser
touch a file.. and then see how guser
can modify it by default (even if the file will still have no-write for group and other).. However guser
cannot write to the directory, so he can't add or remove any files..
P.S. It seems the 'ls' output is confusing.. However, the directory is still 755:
smokey@desk:/home$ getfacl log
# file: log
# owner: smokey
# group: users
smokey@desk:/home$ ls -ld log
drwxrwxr-x+ 1 smokey users 2 Sep 29 17:41 log
smokey@desk:/home$ sudo su test
test@desk:/home$ cd log
test@desk:/home/log$ touch b
test@desk:/home/log$ cd ..
smokey@desk:/home$ sudo su test2
test2@desk:/home$ cd log
test2@desk:/home/log$ touch c
touch: cannot touch 'c': Permission denied