Installing fixture and/or receptacle in beadboard ceiling

The question presupposes that you can't possibly run your new wiring without access through the finished ceiling. If that's the case, you'll want to pull the entire panel and related trim. There's no good way to cut holes in paneling and repair it. You'll be glad you did when your final result looks equally professional.

If you'd like ideas for getting around that task, post a few photos. We may have workarounds to suggest.

As far as cutting for boxes, a jigsaw or rotary tool should do the trick. Spin fast and move slowly to avoid tearout. Remodeler boxes with flyout wings work well.

I would strongly consider conduit (EMT) on the surface as an alternative for a porch application. Painted to match the ceiling it is either fine, because it's a porch and can be a bit less finished than an interior space, or a horror that you/your spouse won't have.

Otherwise, yes, you need to take down the boards (if real beadboard - I suppose that makes me old - but perhaps your house is, too?) or panel (if fake beadboard) to gain access to work behind cleanly. If real boards, you have to work from the correct edge, but you don't need to take them all down.

A third alternative (which might depend on how much this porch is "inside the house envelope" from a HVAC point of view) would be to drywall over it and thus revert it to what you know.