Modifying CipSoft's Tibia game application client's allocated memory during execution in the user space of your own computer is akin to debugging and does not constitute any violation of Copyright or DMCA protections. One could use proxy-injections and intelligent forwarding at the networking level without ever touching their copyrighted program and achieve the same effects. It's a violation of their terms of service if done when in usage to connect to their game-worlds, and their limit of enforcement is merely disablement/modification/deletion of player account data residing on their servers, because technically it's their own property.
When an end user (a player) reverse engineers or does modify/patch the client executable, they and they alone are violating DMCA statute law.
If a independent 'OpenTibia' game-world operator (server owner) is providing a persistent game-world that is basically a clone of CipSoft's game-world template (mapping such as towns and significant unique geographic features, NPC likenesses and story-line/quest dialogue, etc) , then they and they alone are violating Copyright law. Likewise, if they choose to use CipSoft's imagery, identical styling, and/or make use of or reference CipSoft's trademarked names in their brand identity, they and they alone are violating Copyright law.
However neither are relevant as what happens client-side by nature has no bearing on the legal status of running 'OpenTibia' as a network service daemon, nor does any copyright infringing usage by a third party. The game-world network service daemon software projects (OTServ/TFS) contain
0% of CipSoft's source code and
constitute significant non-infringing usage the two paramount factors of the their perfect legality.
Personally, I'd be
delighted if CipSoft tried to sue me. Because I'd have a
certain friend of mine testify and
certain prior-art to exhibit as evidence, and they would get owned for their outright stolen graphics used in older versions of their clients.