I have never heard of this being possible. I know that some counties allow home owners to transfer their property taxes to a replacement property, but what you have in mind is different. Essentially, once you pay off the mello roos, the lien for that special assessment should be removed from your property, and I don't think you can voluntarily put a Mello Roos tax lien back on and get your money back so that you can apply it to pay off the Mello Roos on another property. You will be able to get some benefit from having paid it off because prospective buyers will prefer your property over a similar other property that still has Mello Roos. I hope that serves as some consolation. Double check with the Placer County tax assessor's/collector's offices.