Can I add profiles to an already made loft in SW?
Yes, if at any point you want to edit any feature in solidworks it is super simple.
First: Right click on the desired feature(in this case the loft.)
There will be two menus, a drop down normal one and a floating one above it.
Second: In the above menu there will be an option at the top left of it that will say "Edit Feature" when you hover over it. Click that.
Third: Edit the feature to however you like. Click ok when you are done.
That is all, hope you find this helpful! :)
Better method is to add a plane where you would have want the new loft section to be, then place it above the loft...THEN click on the loft and choose to "add new loft section". While here you can choose that new plane that you created and while here you can also choose to "edit sketch" and see the loft change dynamically.