The faster flash rate is your flashing circuit trying to tell you a bulb has burned out.
My bike has 10watt turn bulbs, a 10 ohm resistor draws 12 watts at 12 volts.
What you want is a resistor that in combination with your led lights draws at least as much as before, a little over is ok, but as I found out the hard way a little under triggers the fast flash rate.
I would leave some headroom in the resistor ratings too. Run a 10w rated resistor at 5w or less.
Assumimg your led lights draw a few watts on their own
Search for 10w wirewound resistors around 15-20 ohms and mount them where they can't melt anything because they will get hot. A few bucks each is about right for the price.
Hope you know how to wire in parallel...