i remember when i used to asked to Skotlex back in the day because he also have the mod of @hidedamage with Filter System, But impossible without the Client Hexing he managed to make it work on 2008sakexe with his last server MouRO.
Unfortunately "NO"
20 years ago? really? kRO was Pre-Alpha Phase at 2002~2003 and releases at 2004 (Official Server)
jAthena (Japanese Athena) translaed to (eAthena) that time was 2004.
It literally says in the map-server.
You don't have the custom script command called "is_valid_item"
it's either it's a command or a functions that checks if the item is costume or not?
This was mentioned back in eAdays, they rejected this and and find useless.
Instead make a strong GRF Encryption Tool since it's more priority than that. since a lot of people broke the algorithm of the tool itself.
Very useful for those who hosted their server under those PRE-BUILT-IN "READY SET GO SERVER"
But self hosted this is useless.
Why would someone let access to your server?
i just realized it was changed, the headers changes as well in this commit: https://github.com/rathena/rathena/commit/5df7de2b15959b234d0b1a73c534b1720e3acc21