I decided to make the mentioned "fix" before my stuff arrived, which should be next week.

And I took a total of two pics, one during and one after, showing the result.

During... Old film going out...

After, showing the result... Or not. The pic is really, really shitty. My phone does this weird noise dither thing with dark photos.

Conclusion: It works!

Considerations for future: Having some form of adhesive for the loose sheet helps a lot.

Thanks again to everyone who helped out!
Now- I'm going to bed. I'm tired outta my skull.

EDIT:

So yeah. I noted that some form of adhesive helps to keep the loose sheet in place. However, take it from me: Not any type of adhesive works.
And this is the story of how I busted that particular sheet of polarizing film. Dumb ass mistake. It's fine though- I was able to save it using the sheet I recovered from the backlight itself, just turned to produce the normal polarization.

I'm sure it'll work out someway, and if it doesn't it doesn't. No real harm done.

Provided this thread still exists later I can post some pics of the whole ordeal along with a conclusion whether it worked or not.

the thickness difference is mainly due to the light guide, which doesn't matter much to you since you only need the polarization film.  which, you can cut with some sharp implement however you need   you'll find its pretty easy

you don't need to trim it to match the shape of the backlight even, just as long as it fits between the light source and the glass comfortably.  the important part is to just make sure the polarization film has coverage over the entire light guide panel.  but, you can trim it to match the shape if you wish.

Like I said, it's just a fraction of a mm, so I'm maybe just nitpicking. With that said, it's only a matter of making two small cuts to have it sit properly.

But no, they're certainly not the same thickness. They're about .6mm difference in size. It doesn't sound like much, but it is very significant when dealing with these tolerances.

*blush* yeah, my bad. My untrained eye said they are "about as thick". I'm new to this after all.

But my main point is still that since I have to remove the polarizing film that is glued to the LED-panel and replace it with the loose sheet, the thickness overall shouldn't change that much. Aren't all polarizing film sheets approximately as thick?

Another difference that springs to mind is that the Kitsch backlight is shaped sort of like a trapezoid at the bottom whilst the nonfinite backlight is a rectangle. So maybe this means I have to trim the film to match that one to make it less mismatched.

But no, they're certainly not the same thickness. They're about .6mm difference in size. It doesn't sound like much, but it is very significant when dealing with these tolerances.

I see your point now.

But if I recall correctly both backlights are about as thick. There can't be a lot of difference, and even if there is a big enough difference so the polarizing film moves or doesn't sit well I'll have to somehow compensate for that.
And failing that, just replace the backlight with another one. But that's the end game solution. I won't go down without a good swing.

Well the kit from Kitsch-Bent sits above the plastic housing as well. If we're talking about the same thing, that is.

Anyway, I won't know for sure until maybe next week when my stuff arrives and I can test this thing out.

No, that's not what I mean. Kitsch's backlights are the same thickness as ours.

I mean the total height of the backlight is lower than the surrounding housing.

Maybe I'm just nitpicking here, but mixing parts actually isn't the best idea. Nonfinite's backlights sit above the LCD's plastic housing, while all other backlights sit below it. So if you use the polarized film from his kit with a thinner backlight, the LCD won't be sitting flush. I'm talking a fraction of a mm here, so maybe it doesn't matter. But I'd still cut a little notch in the corner or cut one side entirely to make it fit better.

Well the kit from Kitsch-Bent sits above the plastic housing as well. If we're talking about the same thing, that is.

Anyway, I won't know for sure until maybe next week when my stuff arrives and I can test this thing out.

Thank you so much for everything (including the backlight, it's really nice )!

the diffusion and polarization film can be cut by scissors if you need to clean up the edges at all.  or a straight razor works well. 

the adhesive strips, if you really want to add these back to hold the film in place, can be replicated by cutting a piece of the thin-type double-sided tape into strips.

the square pieces are rotatable, the 2inch pieces from nonelectronics would work perfect for this (guessing this is your source by your calling them this)

Well. The backlight is actually yours, Kitsch. ^^;

But the polarizing film will be a left-over from a LED panel that I'm planning on putting on the shelf as soon as my new backlight arrives and that film is from one of nonfinite's kits.

If not I will have a 2x2 inch polarizing sheet soon enough and could try that.

Thanks!

You'll want to cut it if you mean a square piece, and not the die cut piece I linked to. 2x2" is too big, the LCD won't sit flush.