My cousin, a Lubavitcher, says both zecher and zeicher (that is, both זֶכֶר with a segol and זֵכֶר with a tzeire) in "Ashrei". I noticed this when I visited him a good few years ago, and assumed it was minhag Lubavitch. In the intervening years I've prayed a bit more in Lubavitch synagogues and have never noticed anyone doing the same, so finally got around to asking my cousin why he does so. He replied that, although it's not in any Lubavitch sifrei minhag, the last Rebbe did it, so he does it.
My question is: Is he right that the last Rebbe did it? If so, is that a good enough reason (from the perspective of a Lubavitcher) to do the same? If not, why might someone; alternatively, if so, why doesn't every Lubavitcher?