all you need for playername is a unique 3 letter (might even work with two, but three is a better habit) string anywhere in their name.
for my name you could use !spam bul rule15
you can also use !list for a slot list or !lookup bul for an @id#
b3 tells you my id # is @157
then !spam @157 rule15
!lookup is not ideal in the context you laid out, but it's an important command for punishing players that leave the server before you punish.
player SuPeRnOoB teamkills someone and leaves before you warn/kick/ban.
you do !lookup supernoob
it returns his id # in the format @###
then you can warn/kick/ban using;
!tempban @199 tk