overriding a magento block in multiple modules (and how to ignore the other ones)

Question

In Magento you can override a block (or helper, or model, etc.) from one module in another one (most common from Magento Adminhtml module). Now I have the problem that I wan

Answer 1

Instead of rewriting catalog_product_grid, why not extend on Symmetrics_DeliveryTime_Block_Adminhtml_Catalog_Product_Grid? That way the Symmetrics module will keep all it's functionalities and you can add yours.

So instead of:

    
        
                Symmetrics_DeliveryTime_Block_Adminhtml_Catalog_Product_Grid
        
    

do this:

    
        
                Namespace_MyModule_Block_Adminhtml_Catalog_Product_Grid
        
    

Of course than a depend in your app/etc/modules file would be fitting.