DiscordSRVUtils Uses a Smart Messages System.
How to set any Discord Message in the Plugin
Any Message in the configurations that is a discord message uses the same way to customize it. If you want a normal Message, write the string normally, but if you want an embed, add the message embed to messages folder. Extension is json. then set the message to "embed:name" do not put json extension.
Depends on the message, for example afk message have "player" and you can use anything after it like "[player.name]". Must be a get method in the Player class, this is an example, other messages like welcome message have "user", "member" and "guild". Any of these must have  and a .something (as i said needs to have a get method in the class)
PAPI is always supported if you have it installed. the player is not set if its not a player-related message, what are player-related messages? Just like AFK Messages
You can test your changes using
/testmessage <message name>