For splitting Terraforming Mars, there are two problems you’ll encounter: The first is that it’s not possible to create projects at the moment; I don’t know why yet. The second is that at least some of the existing modules have irregular version numbers, so you can’t upload them.
On upload, module versions are are checked that they conform to the version scheme laid out by Semantic Versioning. The gloss is that versions have to be of the form x.y.z, with optional trailing pre-release and build identifiers.
The reason for enforcing a versioning scheme for newly uploaded modules is that permitting modules to have arbitrary text as their versions makes it impossible to sort them by version for display. For example: When doing the conversion from the old library, we found some modules where 1.1a was intended to sort before 1.1 (because the a presumably meant “alpha”) and others where 1.1a was intended to sort after 1.1 (as there were also 1.1b, 1.1c, etc. which were clearly subsequent patch releases).
Terraforming_Mars_C221.vmod has version C2.2.1, which doesn’t follow the versioning scheme, so it gets rejected on upload.
If you’re splitting a page where you can’t upload the existing modules to it because they have irregular version numbers, you must have an admin (me) move them once you’ve created the new project page.
In general, if you’re splitting a page and you need to move existing modules to it, you should probably involve an admin anyway so as to preserve file metadata, such as release dates of the files and their publisher, and to avoid having to upload them again.