Yes, with Stihl 1127 series saws, well the same "family" of saws that the MS390 is in, I believe each model or just the 290, 390. Apparently, the overseas version of that saw is factory built with the exhaust modification and carb settings, that U.S. saws do not have.
The modification for this one is done by increasing the air flow which is accomplished by enlarging the holes in the muffler or making additional holes. I am not sure if there are dimensions for the additional holes or increased air flow in total. I thought I saw an overseas factory muffler side by side with a U.S one. In any event, they just enlarge the muffler ports, and the main exhaust port after the spark arrestor, then adjust the carb accordingly. Now some may be able to do that by ear, but I would think a small engine tachometer would be called for to check RPMs after your adjustments. I think with the model I speak of, its 13,000 rpm's max. (don't anyone quote me, just for discussion)
I have seen this modification in more than one forum, and on you tube, however, one should use care in regards to this information and modifying their saw, meaning that carb needs to be adjusted correctly, if not, it could cause engine failure.
In theory its just letting the engine move more air, it should run cooler and provide more service life given the previous. I would also imagine the saw will be louder. I have a 390 and seeing that it was designed to be built with this modification, and is only restricted by U.S. emissions, I would like to do the same to mine, one of the videos on you tube looked simple for the carb adjustment, followed by the saw in use, though I am always skeptical of getting information like this from the web, it appeared to be a simple modification that is beneficial.
Now obviously your Husqvarna is a completely different saw, but maybe its the same situation.
I've used startron and higher octane gasoline, 93 I believe, for the last few years. Prior to that, just the 93 octane fuel, in small engines, and I never encountered any fuel problems to speak of. I think the fuel storage containers are key to this, more than the additives.
Some will use motor oil, used drain oil, personally I just don't like it, it makes a real mess and does not perform like a bar oil should. My father may have used it as I recall. I've seen others use it, not for me. I cut at least 5 cord with my saw annually, so a gallon of bar oil, for me, provides plenty of cutting time, I might use 2 gallons a year looking back, 3 max if I am cutting more than usual, I don't see the value in it. Stihl bar oil is touted to be "environmentally" friendly, as it breaks down. I don't know the specifics on that, but one of the reasons I don't like motor oil is that I actually collect the sawdust and chips in a catch pan, from logs 6" and up and use same for compost and bedding for a few small critters I have, that in turn becomes enriched manure and it makes compost for my small garden patch near the back door and kitchen. There might be traces of oil here and there, but the material I collect seems to be perfectly clean of any oil, dries out and becomes dusty. I enjoy taking byproduct like this and using it, odd to some, works for me LOL !