Digital BW, The Print

Hi all,

I am looking for the common wisdom on replacing ink cartridges on my 
2400 that aren't yet empty. I just received my set of UT-3D inks (all 
cartriges) and I am anxious to try them out since I do mostly B&W. 
However, the current Epson k3 cartriges are still about 1/3-1/2 full.

Do I 

a) suck it up an use up the Epson cartridges until they are empty and 
then switch them

b) Swap them out now, an store the epson ones (in a plastic bag or 
whatever) and use them later.

Thanks for any guidance

Brian