No, it's not advisable. You'll get away with it for a week or so, especially if you've put a drop of Pellgun oil on the top of the bulb to stop the seals drying out, but they shouldn't be stored long-term with CO2 in them because the seals will go.
A good habit to get into is always to finish the CO2 off with more shooting at the end of a session - I tend to favour rapid-fire at drinks cans, especially when the pressure has dropped to the point where accuracy has gone all over the place.