And PB4 is entirely capable of switching profiles without a reload. Pretty sure PB3 was too but it probably had some bugs that made it safer to reload.
I haven't used PB4, but PB3, when I used it, was most certainly not capable of switching profiles without a reload... basic settings like frame sizes and positions were not applied until after a reload. :p
I have no idea, as I don't use PitBull. You'd need to look through its code to figure out which function(s) it calls to update itself when you change the profile. However, I can't think of any situation where you need to change the profile in a hurry, so taking a few seconds to open the configuration window and change it the intended way shouldn't be an issue.
If you're trying to change the profile when you switch specs, for example, you could take a look at the addon Reflux, which lets you set up profiles for addon profiles, and switch between them with slash commands.