Why bother? I doubt that anyone would prosecute you for running 15 watts instead of 10 watts. How are you measuring the power? If you using the average ham meter or even a bird, you would be lucky if you got 15% accuracy. It could even be worst if you reading power while connected to the antenna. Another point is that the efficiency of the amplifier in the radio will vary from band to band. You will probably find that the power is lower on 10 meters.
The best way to be sure is use what ever wattmeter you have and feed it into a dummy load. Adjust your power to the lowest level that you can using carrier power. Connect an oscilloscope across the dummy load. Make the adjustments on the scope so that you can read the level easily. Then switch over to SSB and just use your mic gain so that when you drive the radio its below the carrier point. If you oscilloscope has enough bandwidth you can measure power more accurately than the average ham wattmeter. Its the best peak power reading device you can have in the ham shack. If the radio inspector came and visited you he would probably leave you alone because he would see that you have an oscilloscope and you are doing your best to measure peak power accurately. It would also indicate that you technically minded and know what you doing. Besides the oscilloscope is a handy thing for modulation monitoring to prevent over driving.
Another problem with TS430S is that if you bought it secondhand and dont know the history of the radio, you will probably find some idiot has tried to adjust the radio for more power output. The TS430S
is one of these radios that can splatter pretty badly if some incompetent fool has had his screwdriver inside trying to get more power out of the radio. If you unsure it might be wise to get a real technician to tune the radio for you.
A proper technician could easily adjust the drive level internally to give you 10 watts exactly, its pretty easy to do.
I work a lot of you F calls on 15 meters. Most of these stations are not running 10 watts I know that
I think there are many that are running as much 1kw or more. Because we have all been hams for decades we just know what is possible. Besides the largest number of hams in the world that ran 10 watts were the Japanese hams. I have worked them for more than 30 years, we all know what is possible and what is impossible! Nobody else in the world can run a G5RV or even a triband beam with 10 watts and be 5/9plus. So if these stations are doing it and getting away with it they not going to be concerned about your miserable 5 watts extra.
I must saying imposing a power level as low as 10 watts is ridiculous. They should have made the legal limit 25 watts. This would have been 6db down from 100 watts. 25 watts is enough power for beginners to work the world on any
band if you run a decent antenna. If you cant do it on 25 watts you need better antennas.
I also notice that a lot your new F calls run this bassy ESSB audio, which is the worst TX audio you can run for working DX. I reallystruggle hearing this rubbish crap bassy audio from weak stations. If you reduce the bandwidth of your SSB bandwidth you can increase the signal to noise ratio by as much as 10db. I find it astonishing that they let hams who are supposed to be learning the fundamentals of radio, and yet they allow these hams
to run wide ESSB which is hardly appropriate for a low power SSB station.
I have the kenwood ts440s/at and I heard it goes down to 10 how could I do that and if it only goes down to 15 if I turn down the mic gain to get to 10 from 15