If the particular plan includes park tickets, meaning the Ultimate Park Hopper Pass (length of stay), then no you cannot do it as they will not break out tickets from the package and those length of stay tickets make up a substantial part of the package price.
And you are likely incorrect that it is a good deal. Most find that if you get room separately and then buy those things you want from the pacakage separately, you actually end up spending less than the package price. The packages that are offered year round by Disney such as discovery magic are designed to be convenience packages not discount packages; their prices are generally determined by adding up the regular prices of their component parts with no discounts figured in.