[gmarco]

I think in this way it could be fine to write and it seems to works to

if event == "PLAYER_LOGIN" then 
    local GMEXP_DEFAULTS = { LONGNRFMT = false, SCALE = 1, LIST = true, MAXLIST = 12 }
    for k in pairs(GMEXP_DEFAULTS) do
        GMEXP_CFG[k] = GMEXP_CFG[k] or GMEXP_DEFAULTS[k]
    end
end