It would seem like the preparation process would need to address at least a two or three part challenge; First removing the PU-50, then dealing with the screw holes, and ultimately potentially dealing with deck core issues at the fastenings depending on the water tightness of the fastening penetrations and the core materials. And all of that is before you decide what to do with the non-skid pattern. The closely spaced fastenings would suggest that you probably will not be able to salvage the original molded in non-skid pattern.
Regarding that process, I believe that PU-50 is a family of urethane based adhesive/ sealants. I had not heard of it being used in the marine production industry, but I guess that should not surprise me. In my experience, flexible urethanes tend to make sanding very difficult since they quickly clog sandpaper. That would suggest that you will probably need to use a chemical stripper to remove the urethane. Sikaflex makes a high quality chemical urethane remover that is supposed to compatible with Polyester resins, There are also urethane removers used in other industries like construction. They would probably be more affordable, but I don't know how effective they are and whether they play well with polyester gelcoat, and laminating resins.
The fastening holes are tough, especially if you wanted to end up with a gelcoat or painted (Kiwigrip) deck. My guess is that they will need to be reamed open and filled. That can probably be done with thickened polyester if you are overcoating with a waterproof material. But getting a good seal and stabile adhesion won't be easy.
Of course things get way more complex and expensive if of the fastenings have been leaking and the core has become damaged. The worst part of that is that you probably cannot fully detect that condition until the teak has been removed, and at that point, there is no turning back.
Maybe 30 years ago, I faced addressing a similar problem on a small race boat with a slew of abandoned bolt holes in the deck and very ineffective non-skid. For a while I leaned towards grinding down the original non-skid gelcoat to a level and fair surface., I was planning to apply new gelcoat to the deck and use Gibco Flex Mold
Gibco Flex-Mold, Non Skid Surfaces to create a factory looking gelcoat pattern. Gibco makes both male and female molding materials. I was considering the female molding material, where you troweled on gelcoat, then rolled the female material over the wet gelcoat to mold in the non-skid pattern.
I decided that it was a great way to go, but that the boat in question was not worth the expense and effort (i.e. resale value of less than $3-4 K). We ended up filling the holes with thickened resin (I don't recall whether epoxy or polyester) and simply painting the deck with a scattered sand non-skid. It looked okay and was a vast improvement over the original non-skid, but I don't see that as an optimum way to go on a more valuable boat because it definitely looked like a after the fact solution rather than a factory, or high end post production solution.
Jeff