When you're not injured?

Listen to your PT. If there's a refund or transfer available for your A race then use it now, and then give yourself time to heal properly before racing again. I wouldn't enter another race until it's fully healed (unless you have the option to postpone your 2018 entry to 2019 which I guess is far enough away). Nothing more frustrating than having the days ticking down to a race and not being able to train properly, and if you race when not fully healed then it's pretty much inevitable that you're going to flare the injury up again and could be off for a long time.

If you can't get the entry money back then I guess you could always do the swim and bike and then call it a day. I did that once when I had a long-term running injury (mine was hip) which didn't stop me from swimming and biking, I was getting so frustrated that I decided doing 2 thirds of a race I'd already entered and then cheering on my friends during the run was better than nothing.

I am just now getting over high hamstring tendonitis. It can be a very stubborn disease, and can become much more long term (chronic) if you do not take the steps to treat it NOW. Mine has taken over 3 months and I am still not back to running. For me, I had to stop all activities (Swim, bike, and run). When you bike, you are sitting on the area of your "sit bone" (ischial tuberosity). This is where your hamstring tendons attach and will remain irritated with continued cycling. It may not prevent you from healing but it will certainly slow it down.

So, long answer but YES 100% you should consider deferrment.