L3pro rgbic

Hello, I have one short question whether the L3 pro tapes can be extended ?

I don’t think so, according sonoff official web page, there is only one standard which is 5M/16.4ft on sale, no extension available.
But ask sonoff custom service would be the better way to get accurate info.

Yes, you can. There is a setting under configuration called LAMP BEADS SETTING where you set the number of LEDs of your strip. Do not know the limit but that is the way to achieve that.

How many beads can it be set to ?

For what I can see, the app is restricting the range beteeen 20 and 150 beads.