Even if you change the processor affinity, it probably wont work.
Programs use something called Mutexes, and those work across all processors. It keeps only one instance running since the call to open the mutex section (MUTually EXclusive) blocks or returns a failure code when entering a MUTEX that is in use. Also like a semaphore, etc.
If you dont have access to source code, or a way to undo the mutex, it can't be done.
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