I am in need of some advice/pointers on how best to attack a problem I am faced with in Magento 1.4.0.1.

Here is the scenario: Consider a product catalog of multiple thousands of products in which there are many and various retail markup percentages. There is a need to sell some of those products to other retailers, and I need a way to easily categorise them into percentrage markup groups, so that the other traders can easily purchase items from us without needing to call and confirm pricing.

All products prices are added to the magento database including VAT - so the actual retail value is the starting point.

I think this needs to be done by adding an attribute on the products that determines the maximum discount level that can be applied to any given product.

Obviously, this would entail a massive amount of work to update every product.

Is there a way to achieve what we need that I don't yet know about (within Magento)?

Can single attribute values be mass-populated somehow, without affecting other attributes such as name/description/etc?