If both drivers have the same name then yes, one will copy over the other. The only suggestion I can make will be to name one driver something like HP1 then re-install the same driver and name it HP2. It should work. Before you start printing you will have to go into the printer driver folder and click on the one you wish to use for that particular session by making it the default driver.
you would want to install separate instances of the same driver - there's no possible advantage.
The driver runs the printer, and if you want a draft copy you select 'draft'in the printer dialogue before you print. Likewise, you select 'colour' when printing colour images - text will print in black whatever setting you choose, unless you have coloured some of it of course.
Every time you try to install another instance of the same driver it will simply overwrite the first one, so leave it at one copy and work from there - that's what everyone else does.