Can I re-fluff blown-in fiberglass insulation with a cellulose blower?
Whether you can or not, you probably don't want to. If you're going to go through the trouble trouble of pulling out the fiberglass, you might as well just replace it with cellulose, which has a significantly higher R-value (around 50% higher per inch than fresh loose fill fiberglass). Your settled fiberglass, on the other hand, has a significantly higher R-value per inch than the fresh fluffy stuff! The settling of loose fill insulation is only a problem because you lose inches faster than the R-value per inch increases. "Fluffing" what you have now would save you a little bit of cellulose but if you still fill to the same depth, but would leave you less insulated.