2 added 81 characters in body
source | link

Not tested, but it should work ..You can check in admin config section if your module is disabled. If it's disabled return value of rewritten method.

class Your_Module_Model_Xyz extends Another_Module_Model_Xyz
{
    public function methodYouWantToRewrite()
    {
        if (!Mage::getStoreConfigFlag('your/config/path')) {
            return parent::methodYouWantToRewrite();
        }

        // You code ...
    }
}

Not tested, but it should work ....

class Your_Module_Model_Xyz extends Another_Module_Model_Xyz
{
    public function methodYouWantToRewrite()
    {
        if (!Mage::getStoreConfigFlag('your/config/path')) {
            return parent::methodYouWantToRewrite();
        }

        // You code ...
    }
}

You can check in admin config section if your module is disabled. If it's disabled return value of rewritten method.

class Your_Module_Model_Xyz extends Another_Module_Model_Xyz
{
    public function methodYouWantToRewrite()
    {
        if (!Mage::getStoreConfigFlag('your/config/path')) {
            return parent::methodYouWantToRewrite();
        }

        // You code ...
    }
}
1
source | link

Not tested, but it should work ....

class Your_Module_Model_Xyz extends Another_Module_Model_Xyz
{
    public function methodYouWantToRewrite()
    {
        if (!Mage::getStoreConfigFlag('your/config/path')) {
            return parent::methodYouWantToRewrite();
        }

        // You code ...
    }
}