I have information for mods of 3 different BMW flashers to slow them back down after installing LED lights, including the newer unit on my 2006 LT.
Correct replacements will actually end up being as bright as or brighter than the original bulbs.
Various people have commented that my LED turn brake and tail lights are very noticeable. I got the tall 1157 equivalent from Superbright LEDs. They fit everywhere on the LT just fine. I also replaced all the other bulbs with LEDs. The small LEDs on either side of the high beam are much brighter than the little bulbs that were there. If you need help on sizing up replacements, I'd be happy to help.
I added a jumper to the middle bulb to have the brake filament on it light up with the brakes too. This doesn't effect the tail light bulb notification, but on my 2006 LT it did get rid of the high frequency flickering of the LED brake bulbs. There must be something in the brake circuitry that pulses the brake light circuit. Not fast enough to make a bulb glow, but the LEDs will flicker.
2006 BMW K1200LT purchased June 2014, and loving this thing so far!