Pertaining to preflight scripts. Does it just check for the variables, or actually add / change them to the file to print? (Like bleed, crops, etc)

tFLOW ES > *tFLOW FAQs
Some of the variables you can set to check the file (such as checking the resolution).  These variables will add warnings in your preflight report.  Other variables will actually change the file (such as adding the bleed).