I did this when I first started and it worked fine for me. I used similar flavors in the carts I was refilling, tobacco with tobacco, and sweet with sweet. I got some serious milage out of my carts, and did not feel bad when i tossed them since I used them several times. I graduated to a clearomizer tank type system now, I DO use a ciggalike at work, since the bigger one not very discreet.
Trial and error, try what works for you, you can find loads of informational videos on youtube, just search, cartomizer, refill ecigg etc.