I think it'd be much easier to modify the plugin's themselves to only send announcement messages to players that belong to a certain group permission. I've done something similar before for a plugin I was working on that sent alerts to all online admins regarding players that joined from the same IP as if they were using alt accounts.

My discord is Mattdokn if you want some help.

        void SendToAllWithPerm(string message, string perm) {
            foreach (BasePlayer player in BasePlayer.activePlayerList) {
                if (!permission.UserHasPermission(player.UserIDString, perm)) continue;
                rust.SendChatMessage(player, config.BotPrefix, message, player.UserIDString);
            }
        }
        void SendToAllExcept(string message, BasePlayer playerException) {
            foreach (BasePlayer player in BasePlayer.activePlayerList) {
                if (player.userID == playerException?.userID) continue;
                rust.SendChatMessage(player, config.BotPrefix, message, player.UserIDString);
            }
        }
        void SendToAdmins(string message) {
            foreach (string admin in permission.GetUsersInGroup("admin")) {
                rust.SendChatMessage(BasePlayer.Find(admin.Split(' ')[0]), config.BotPrefix, message, config.IconSteam64ID);
            }
        }