To change the client version means to change the protocol, the protocol is written in the sources, so you would have to change a lot of code in C++ to make such a change, and we are talking a major amount. You are better off finding an engine specifically for 7.4

The code exists as free and open source code already. If you however wish to pay for my services installing this system into your current server, I might be willing to do that for a price. You can find and message me on otland.net with the name Codinablack to discuss further.