The only thing I ever did to get all the 4th jobs from re to pre-re was just copy and paste everything from the 4th jobs into my import skill.db file and made sure that they appear in the skilltree.yml.
put this at the bottom of your pre-renewal skill.db file and then make sure it shows up in the skilltree for example: assassin
I removed the requirements for the skill so I can get it with @skillall
and again make sure that you have the cliendside for the skill otherwise it will glitch out. Thats all you should have to do to get the skill working for your class.
if its still not working after that it might have to do with the version of rAthena you are using and if the 4th job skills are in there or not.
If that still doesnt fix it then I can't help you, sorry 😞
Load up your Server in the "Server Database Editor" and Look for "Item Combo" and delete the first line that says "MO_EXTERMITYFIST".
if you dont use Server Database Editor you can go into:
db/re(pre-re if used)/item_combo.yml and do the same there.
Check either of those 2 files located in either re or pre-re DB folders and check for the entry with the ID: 4 and see if its there. If its missing you might have to copy it over or create your own
Also check if the script you are using is actually correct