I think I undertood what you are trying to do: Keep test id same while copying test cases from one QC project to another (maybe as part of upgrade from one version to another? or just consolidation of QC/ALM projects?)
This is not possible if you are referring to internal Test ID given by QC
If you are talkign about some ID that you yourself create/maintain on a QC/ALM project then yes you can keep it the same.
