I know for sure that it is possible to make a NOGCD(global cooldown) hack working on 1.12 servers which have no serverside check
I found the 3.3.5 NOGCD hack release page and the tutorial about how to make it able for all versions
however, the url there was 'invalid'(may have broken because of such a long period of time)
I knew it was easy to make
Really looking forward to a working GCD hack on 1.12.1 servers!