Basically, to remove the old inks, just grab a syringe and suck as much out as you can, then run a head clean. The put the new ink in and run a few more head cleans (hey, ink is cheap through a CISS) and your new ink should be starting to feed through just fine. That's all you can really do.
I say go for it personally. The comments so far are right but personally, I always purchase a CISS whenever I get a new printer. Makes it easy in the long run. I personally hate refillable cartridges so it's CISS all the way for me.
For the OP, use a waste ink kit from Octoinkjet.co.uk. I bought one a short while ago for my Artisan 725 and it's super easy installation and solves your problems. Plus he gives you the proper reset tool that the techos use, rather than the annoying retail one you can get and have to register...