A small portion of the back of my starboard side bunk has worn through. I can see a small amount of wood. I ordered a roll of new carpet. My question is, should I remove the old worn portion and then put the new stuff on or can I apply a new portion right over the old stuff?  I obviously can’t access it while the boat is on my trailer so I’ll have to launch, tie up the boat, and then fix it at the access. Anyone ever done this and how did it go?

I did mine this past weekend. Went to one of the less popular ramps and it took a little over 30 mins. The new carpet was thinner so I just went right over top...I guess time will tell but it looks fine.

Made new bunks at home then went to the closest boat ramp and beached the boat and replaced the bunks.

 

Like @kjfishman I have done this twice. I bought new lumber and carpet and made the new bunks at home. Took it to a boat ramp and tied off the boat. My wife usually goes with me and fishes out of the boat while doing this. I take a cordless drill with me to drill bolt holes in the new bunks. Be sure to not let the bit go all the way through. I only had three bolts on each bunk so it didn't take too long. I also had new bolts and washers to use. I did not use any old material back.

I've replaced mine in the garage.  I just use a car jack to raise one side of the boat at a time.