Hi,
It is an interesting and challenging job.

This is just something to consider:
After reading all the instructions I found it almost impossible to get the thing out without damaging it at all. If I had to do it again, rather than excessive continued attempts to get it out completly intact, i would , instead, pick a spot, like in the driver side corner, and bend it, or even break it, in a way, so that once you get it back in it wont be noticed.
I say this because I feel that in a continued effort to get it out with out " any damage" You could possibly be putting the backboard at higher risk of catastropic damage.

I dont recommend this bending , or breaking, as a first strategy, because others have reported successfully removing the beast without damage. But I think this would be a worthy addition to your considerations, IMOP.

We changed our headliner a few years ago. wouldnt hesitate to do it again. Its and interesting job.

The glue has since come loose in a few places, but we use "screw pins" with excellent results, and we remain happy with the results.

good luck with your project.