Probably something someplace is picky about versions.
I found that I could replace the k_delft.rpm with a later one without obvious problems. I needed that because the kernel on the CD was so old that it could not use the network interfaces. But it is risky to do so.
Under the covers YaST runs rpm with closed eyes (e.g. --nodeps) and relies completely on the dependency tree recorded in some other files. The check on disk space also uses those other files.
AFAIK the tools to create those index files and cross references is not part of the distribution, and the format of the files is proprietary. You may be able to hack it by looking at the files, but you never know if you got all the bits right. We decided to avoid YaST in our installs. Initially we build the system through a bunch of rpm commands to create the basic structure, and then add the rest of the packages with apt4rpm. This way you create a new server with current versions rather than start with old code and upgrade that for each server before you can use it. The process also allows us to create much smaller servers with far less packages. We did find that many of the SuSE packages are a bit sloppy on the dependencies, so it takes some tweaking and hacking to get all right.
Rob
