The reason for different amount of leds per pin is because I have different amount of leds per window with difference of about +-50 leds. Having the same amount means extra wiring and cutting the strip of one window in the middle in order to start signal from another pin. But from what I undertand if I put MAX let's say 400 leds and some pins will have 360 or 370 leds it won't be a problem. Only if I send a slow wave it there will be a small delay jumping from short strip to the next one because it will be calculating 371, 372, 373 etc which are non existent, correct?
There’s no way to specify the number of LEDs per pin, but if you just start the object with the max LEDs that one pin has there’s nothing stopping you from using less LEDs on the other pins. You just have to make sure that what ever is drawing to the LEDs isn’t trying to update LEDs that aren’t there, it won’t cause any problems if you do try to do that because of the nature of the shift registers, just know that nothing will happen if you try to write to an address that doesn’t have an LED. Of course the simplest option is to just keep the number of LEDs per pin as close as possible, I can’t think of any reason that would benefit from having a varying number of LEDs per pin.