The concept of configurable products is designed to cater the catalog wherein a product has multiple options, once you select and change any options, the product specifications, description, price, image etc changes.
To be descriptive, imaging you have a product such as guitar. When you select a dropdown for type of wood, there is a total new specification for that guitar and price. Now you change the no. of strings from 6 to 7, there is a whole new product with different specifications. This is where configurable product with association concept comes handy.
However, magento has built a different way for products in which if you change the option, only price changes but there is no change in specification, description, images etc. This can be done using "Custom Options" tab.
This is useful in situations for example, you have a medicine ball to cell. A 50 inch medicine ball and a 80 inch medicine ball looks same in image. Also majority specifications are very similar. Its just when you change the diameter, just price changes. This is where you can use custom options.
Last but not the least, if you want to change anything from magento core, do not directly edit the core files. Override the required file into local. In future if any issue arises, you can disable your overriding just from local.xml and check if core is working. Here is a link for overriding : http://inchoo.net/magento/overriding-magento-blocks-models-helpers-and-controllers/