Not quite sure what you mean...'will my new traffic become my downloaded planes in FSX ?'
If you've just downloaded new planes, then no. FS does not automatically generate AI flights. All flights are 'programmed' in a file, sometimes referred to an AI Traffic file. It/they contain the 'flightplans' for every AI flight.
If you're unfamiliar with AI traffic files, download Traffic Tools v2.02 from
http://www.simviation.com/fs2004utilities1.htm. It's for FS2004, but the concepts described in the help file, 'Readme.htm',
At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation.