With a large enough order, having custom cells made wouldn't be a problem. The issue would be getting the old cells out. From what I saw when I took my pack apart, it looks like it might actually be cheaper to just build new modules from scratch:
Not only is every cell spot welded(?) 3 times, but the frames themselves are all heat staked together. With the right tooling to disassemble and assemble packs quickly, it would probably be possible to turn a profit, but the time and resources required to get started are prohibitive for most.