Heffe yeasts live fast and die young. I'd leave a Hefe well enough alone, for others the best time for yeast harvesting (in my understanding) is at high krausen due to the large amounts of healthy yeast.
I haven't heard of anyone cropping to impact the flavour profile. I would imagine that any yeast removed would be replaced by the other yeast dividing. I guess if you pulled the yeast off late enough in the ferment there might not be enough residual oxygen for the yeast to want to multiply so the existing yeast would struggle on, probably producing similar flavours to underpitching. The downside being you've opened the fermentor and thus increased the chance of infection, the yeast in the later stages is struggling against the growing alcohol percentage, so removing too much yeast may result in a stalled ferment. Also at such a late stage I can't see there being a lot of sugar left for the yeast to process, so flavour impact would be fairly marginal, kinda like heating the ferment up in the final stages doesn't produce the wild esters that can be created if heated at the start of the ferment.
Just my musings...