In theory if you have two sets of raw expression sets, from the same array model, then you can simply bind one to the other (accounting for the probe location). However, doing this creates a whole world of problems. There would have to be a very good justification for doing this. The first problem is that there will be a batch effect between the two datasets, as previously mentioned. If you manage to correct for that successfully then, you might get some meaningful data out of the analysis, might. This is a post experimental design decision and is not recommended.