Stewart, assuming you have an A-6, twist harder. If you dont know the history of the boat in question there is a chance someone glued the valve or over wrapped it in teflon tape. Pumping the floor up stiff can help give you something more stable to twist on. If it is on an aire floor bladder those can be a real bitch. Pliers on the back of the valve is a bad idea. Ive repaired plenty of those. Worst case scenario it needs to be carefully cut into pieces to get it out.
Billy, I'd lean towards buying the pressure you want instead of risking the spring experiment. If your valve is new not only should it have a dot, but also should have the pressure stamped in the the body of the valve. Below is the link to the pressure chart.
Likely the root cause of the blown v tape wasn't the brown dot PRV. Any healthy floor should be able to take 2.5psi no phase. I have done the v tape on many a hyside that still had the yellow dot PRV. Typically water in the floor that has steamed over time (even if none is present when the floor blows) is the culprit and its somewhat common in boats purchased from outfitters. A lot of guides dont know or give a shit if they get water in the floor; its not their boat. I have also seen floors that just had weak spots where the glue didnt bond well to one side of the floor or the other. It is especially common in the hysides from 2000. The last 4 that I did, including the one I just finished up today, were all 2000 boats.
By all means if you think you have a weak floor, run a yellow dot and run it soggy. If you dont want to manage your floor pressure run yellow or blue. I'm not telling anyone to buy a stiffer PRV. I talk with customers about what they want and depending on what they say they end up with blue (2.0) or brown (2.5). I run white (2.75) in all my boats (even my 86' Avon) and just plan on managing the floor pressure myself, typically a little soft in gear boats. As I said above, I never let my PRV's blow off and relying on your PRV to tell you when to stop pumping is the best way to have a leaky PRV, or blow up your floor. The PRV can also only let a little bit of air out through the hole so if someone goes hog wild on a barrel pump and doesn't realize the PRV is blowing off they can bring the pressure up faster than the PRV can let it out. Next thing you know, blown I beam or v tape. I see the job of a PRV to let air out of the floor if it slowly sees a pressure increase due to temp, that is all I am counting on it for, and even then only if I overlook it.