The partition capacity is divided in a number of logical sectors between 32769 and 65536 with a sector size power of 2. For example, a 320GB partition is divided in 40960 sectors of 8MB. It's possible to write a tool to change the number of sectors, but it's impossible to change the sector size. So you can only expand it to the next power of two (in the previous example up to 512GB)
But no one has created this tool.