Headlights are normally rated by hours of use. The HS1 is listed as having a 700 hour life expectancy. With the low out put of a P250's charging system, it would seem that a 65 watt bulb would be stressing the system, and possibly lowering the output to charge the battery. Not a good thing.
www.candlepower.com lists the HS1 bulb from a German company, Narva and explains the difference in the prongs between an HS1 and an H4 bulb. They are different, and while they may work ... there is an alternative. Somewhere on Candlepower's extensive web site, there is an H4 bulb which has an output rated at 65w but the draw is 35w. A good thing. The downside, the bulb costs over 40 bucks, I went with the 35w bulb at 14 and some change.
This is a huge web site with a lot of information imbedded in it and it does take awhile to blunder around on until you find what you're looking for. I also found some really difficult to find, six volt bulbs for a few of my old, crusty Italian and English bikes which are normally listed in the unobtanium catalogue at your local Stornello dealer - final note, with regular shipping, UPS ground service from Maryland to Chicago, it took three days to arrive. If you do order from them, get a few bulbs at the same time, with Kymco's the bikes will definitely outlast the bulbs.