I typically will use a good amount of fasteners and will also set up parameters to pass variables to either sensitivity or optimization studies. For example, I may want to vary fastener diameter, etc. No problems here as a real number as a parameter value is straight forward.
If I wanted to run a simulation (Creo3, M020) with or without preload I'm not aware of the method to setup a parameter with a "yes/no" condition based on the menu pick (check box for preload).
If I had just a few fasteners, I'd manually edit them....but when you have a lot of them this can take a while. You also can't define preload as a named parameter and define it as zero for the no preload condition.
Thanks,
Scott