This is possible, but it is not clear if it is a good idea.

If your computer has more than one CPU (or a strong CPU with hyper-threading) and a lot of memory, you can try do run more than one ENVI-met. You have to make your own mind if this more efficient than running just one version and do other things on the same PC.

If you have only one (classic) CPU, don't run more than one ENVI-met at a time. The programs will block each other and prevent an effective execution.