[CrazY.]

In a way yes, but I am not sure about the performance while working with a big number of data inside the file. You could save player's authid as section and organize the data between the keys.

new const FILENAME[] = "player_data.ini";

SavePlayerData(this)
{
    new szAuthId[MAX_AUTHID_LENGTH], iMoney;

    get_user_authid(this, szAuthId, charsmax(szAuthId));
    iMoney = cs_get_user_money(this); // e.g. 16000

    ini_write_int(FILENAME, szAuthId, "Money", iMoney);

    /* Result:

    [STEAM_0:0:0000000]
    Money = 16000

    */
}

LoadPlayerData(this)
{
    new szAuthId[MAX_AUTHID_LENGTH], iMoney;

    get_user_authid(this, szAuthId, charsmax(szAuthId));
    iMoney = cs_get_user_money(this);

    ini_read_int(FILENAME, szAuthId, "Money", iMoney);
    cs_set_user_money(this, iMoney);
}

Update is already implemented. ini_write_* adds the key and value if the key does not already exists, otherwise it update.