Hey, I don't know if this already exists somewhere, at least I didn't find it even when I was searching for a guide on this.
So if you are in the same position I was in, and you wonder how to add a new client version to your list (like you want to play 10.78 and it doesn't exist in the list) then you simply just go into otclient\modules\gamelib and open game.lua (use notepad, notepad++, normal text document opener or whatever) and then go down to the line where it says this: "function g_game.getSupportedClients()" then you just add the version number you want. after the last one.
Of course you'll have to add a map called 1078 in the "things" map and also the .data and .spr of the version like you usually do to play!
So if you are in the same position I was in, and you wonder how to add a new client version to your list (like you want to play 10.78 and it doesn't exist in the list) then you simply just go into otclient\modules\gamelib and open game.lua (use notepad, notepad++, normal text document opener or whatever) and then go down to the line where it says this: "function g_game.getSupportedClients()" then you just add the version number you want. after the last one.
Of course you'll have to add a map called 1078 in the "things" map and also the .data and .spr of the version like you usually do to play!