Your birth plan will be (1) bespoke to YOU and (2) decided primarily by YOU. There's not a rule that says "high BMI means we do X", there's more like, "This person has high BMI plus x, y, z so altogether this is the consultant's opinion on the best way forward" or "This person has high BMI but there are no other issues so X is a realistic option for them".
You have the right to say no to everything they suggest. You have the right to ask why. You may, or may not, have other risk factors, but they are only risk factors and not concrete reasons for anything. For everything you should use your BRAIN
Benefit (what is the benefit to me, what is the benefit to baby)
Risk (risk to me if I go ahead, risk to baby)
Alternatives (what else could I do instead, what can I do to reduce my own risks)
Intuition (does this feel like the right decision)
Nothing (what happens if I do nothing and just wait and see)
In my case I am just under 30 BMI (or, I was below it at booking) but am also of advanced maternal age and also classed as IVF as this is a donor embryo. This collection means there's a host of things "more likely" to happen like gestational diabetes, pre-eclampsia, stillbirth, etc. In the beginning the first consultant was an absolute cow and completely dismissive everything what I wanted, I moaned to the midwife at my next appointment and she completely backed MY decisions up, helped me educate myself to make an INFORMED decision, and made it clear that actually? I have no risk factors that are significant at all except for my age. Everything else is only a statistic and they have not happened in my case.
You will probably find this is the case. Every time they say "high risk" ask them what the ACTUAL risk is (for example if you're 5% higher chance of something, that's a 95% chance it won't happen, so you then think about whether the "risk" option is a real problem for you, and if not, you can choose to ignore it).
As for weight as others noted it's not recommended to go on drastic weight loss BUT maintaining your weight might be appropriate - which then equals a 9-12kg loss because that's what baby, uterus, boobs weigh etc. Ask if they will refer you to a dietician. You will find late pregnancy tough going while on the heavier side (I completely misjudged it! but you have more time left than me) and increasing your fitness is likely to make it easier, including the birth.