Sory, but I've read this several times now and still can't make head nor tail of it.
...What I'm trying to do is create a 'adjustable frame'...
...Its 'an' adjustable frame but ok....with you so far...
...a top layer that acts just like a picture frame would for an actual picture...
...so...nailed to the wall then?
...I'd like to be able to re-size this frame so I don't have to keep re-cropping/filling the areas every time I make a change...
Right....most of this needs clarification...re-size in what way? What is 're-cropping' and to what exactly are you doing it to?
'Filling'...? Filling what?
What are these 'changes'...?
...I've tried looking into how to accomplish this, but between layer masks, vector masks, shapes, shape masks, paths, and clipping masks, I'm so confused as to what to do at this point...
I'm confused too.
I can kind of, sort of, read between the lines and almost decipher what you need but I'm struggling to comprehend what it is you have, what you are doing to it and why you feel the need for something as complex as 'adjustable'.
From the image it 'looks' like you just need a 'Stroke' around the image which is not exactly difficult to do and yet it seems far from anything you describe.
Can you be a little more descriptive in what it is you have, what you need to do and why adding a 'Stroke' wouldn't do exactly what you want.
Sorry....it may be a clear as day to you, but it's as clear as mud to me.