Personally, I am happy if I can get my saws to start and run 'stock' (as designed by the manufacturer) reliably. And for me, a MS 660 has more power than I typically need, so I would not need to modify it.
I get the idea of increasing performance from a saw, of improving it's power to weight ratio, etc. But I am not a two-stroke expert to know where the limits are, and when the life of the saw is compromised, when a uniform torque band is sacrificed for a higher peak torque at high revs, etc. I don't want a saw that is tuned to it's edge, I want one with a wide comfort margin that is forgiving if the fuel is not blended exactly right or the air filter is a little clogged, etc.
There are people on this site who actively promote modifications and performance gains. We hear about 'work mods', and 'race mods', etc. What we don't hear so much about are people that ruin or damage a saw (and dump it on eBay? Craig'sList?, etc.). It's one of the reasons I am cautious about buying a used saw that someone may have experimented on.
You have worked hard to acquire an 'almost new' saw. If you decide to modify it, I would proceed cautiously, and only after you have worked with it for a while in it's current condition. You may find that it is 'good enough' for you as it is.
Just my opinion. Others with vary.
Philbert