I have a 2012 F150 FX4 and planning on using a Add-A-Circuit tap to my passenger side fuse block. Will this tap still allow me to snap the fuse block cover back on?

 

I used one for my led footwell lights. I had to trim the cover to accomodate the wire. Once you've got your project done, trim off a small amount at a time and keep test fitting the cover until you have the minimum amount trimmed to get it to snap back on.
And by the way, even though my kickpanel fusebox has the micro size fuses and not the minis, the mini fuse holder is the one I needed to use and the prongs fit in there perfectly. The micro holder would not have worked due to a clearance issue with some part of it. Kind of odd but that's how it worked.

 

Does the spare fuses have 12 volts available? I could use the add-a-circuit in one of unused circuits.

Or best option would be to locate the wire that is associated with one of the spare fuses, assuming one exist. Can anyone comment on this idea?