Customize cart template in existing magento theme

Alter a existing magento theme 1.x. There needs to be done some changes in the template of the shopping cart. An alternative display for bundle products. An alternative summary block. There should be only sum including tax and tax (summary). This alternative summary block should be configurable over an additional extension. Important!: No changes on core files. The native layout xml logic should be used as far as possible. Github account necessary. testing server will be provided by us.