freitasm: If you reinstall Crashplan or install on a different PC, providing the data has the same path you can take over ownership of a previous backup and nothing is uploaded.
If you change paths, well...
That is part of the problem. The home server name is the same but the path is different however on the Crashplan site it seems to imply that it will still handle that.
Data De-duplication: This data de-duplication happens at the block level, so even repeated information within a file, as well as across all files, is not backed up unnecessarily.