ShippingMethod field on Order table => Foreign Key?

I want to change the ShippingMethod field from string to int ( & rename to ShippingMethodId) and point to primary key in ShippingMethod - table.
Reason: I am writing an integration app for quickbooks and need to add the shipping costs to the sales order - allocating to the different shippingmethods.
Downloadable products dont require shipping so the Foreign Key would be null in Order table.

Any reason I should NOT do above - any chance of it being accepted in the active branch ?

Thanks
piet

You're talking about offline shipping computation. Not all shipping rate computation methods return shipping methods defined in admin area (Admin area > Configuration > Shipping > Shipping methods). Some store owners could use real-time shipping rate computation methods such as UPS, FedEx, USPS (there aren't appropriate shipping methods in the database in these cases)

Thanks - I am not familiar / experienced with the real time computations.
I have implemented a lookup as a workable solution.